Avoid meta programming to initialize functions in module scope (#26388)

I'm trying to get rid of all meta programming in the module scope so
that closure can do a better job figuring out cyclic dependencies and
ability to reorder.

This is converting a lot of the patterns that assign functions
conditionally to using function declarations instead.

```
let fn;
if (__DEV__) {
  fn = function() {
    ...
  };
}
```
->
```
function fn() {
  if (__DEV__) {
    ...
  }
}
```

packages/dom-event-testing-library/domEnvironment.js

@@ -13,7 +13,7 @@
  * Change environment support for PointerEvent.
  */
 
-const emptyFunction = function () {};
+function emptyFunction() {}
 
 export function hasPointerEvent() {
   return global != null && global.PointerEvent != null;

packages/react-dom-bindings/src/client/ReactDOMComponent.js

@@ -94,15 +94,8 @@ const HTML = '__html';
 let warnedUnknownTags: {
   [key: string]: boolean,
 };
-
-let validatePropertiesInDevelopment;
-let warnForPropDifference;
-let warnForExtraAttributes;
-let warnForInvalidEventListener;
 let canDiffStyleForHydrationWarning;
 
-let normalizeHTML;
-
 if (__DEV__) {
   warnedUnknownTags = {
     // There are working polyfills for <dialog>. Let people use it.
@@ -115,15 +108,6 @@ if (__DEV__) {
     webview: true,
   };
 
-  validatePropertiesInDevelopment = function (type: string, props: any) {
-    validateARIAProperties(type, props);
-    validateInputProperties(type, props);
-    validateUnknownProperties(type, props, {
-      registrationNameDependencies,
-      possibleRegistrationNames,
-    });
-  };
-
   // IE 11 parses & normalizes the style attribute as opposed to other
   // browsers. It adds spaces and sorts the properties in some
   // non-alphabetical order. Handling that would require sorting CSS
@@ -133,12 +117,25 @@ if (__DEV__) {
   // in that browser completely in favor of doing all that work.
   // See https://github.com/facebook/react/issues/11807
   canDiffStyleForHydrationWarning = canUseDOM && !document.documentMode;
+}
 
-  warnForPropDifference = function (
-    propName: string,
-    serverValue: mixed,
-    clientValue: mixed,
-  ) {
+function validatePropertiesInDevelopment(type: string, props: any) {
+  if (__DEV__) {
+    validateARIAProperties(type, props);
+    validateInputProperties(type, props);
+    validateUnknownProperties(type, props, {
+      registrationNameDependencies,
+      possibleRegistrationNames,
+    });
+  }
+}
+
+function warnForPropDifference(
+  propName: string,
+  serverValue: mixed,
+  clientValue: mixed,
+) {
+  if (__DEV__) {
     if (didWarnInvalidHydration) {
       return;
     }
@@ -156,9 +153,11 @@ if (__DEV__) {
       JSON.stringify(normalizedServerValue),
       JSON.stringify(normalizedClientValue),
     );
-  };
+  }
+}
 
-  warnForExtraAttributes = function (attributeNames: Set<string>) {
+function warnForExtraAttributes(attributeNames: Set<string>) {
+  if (__DEV__) {
     if (didWarnInvalidHydration) {
       return;
     }
@@ -168,12 +167,11 @@ if (__DEV__) {
       names.push(name);
     });
     console.error('Extra attributes from the server: %s', names);
-  };
+  }
+}
 
-  warnForInvalidEventListener = function (
-    registrationName: string,
-    listener: any,
-  ) {
+function warnForInvalidEventListener(registrationName: string, listener: any) {
+  if (__DEV__) {
     if (listener === false) {
       console.error(
         'Expected `%s` listener to be a function, instead got `false`.\n\n' +
@@ -190,11 +188,13 @@ if (__DEV__) {
         typeof listener,
       );
     }
-  };
+  }
+}
 
-  // Parse the HTML and read it back to normalize the HTML string so that it
-  // can be used for comparison.
-  normalizeHTML = function (parent: Element, html: string) {
+// Parse the HTML and read it back to normalize the HTML string so that it
+// can be used for comparison.
+function normalizeHTML(parent: Element, html: string) {
+  if (__DEV__) {
     // We could have created a separate document here to avoid
     // re-initializing custom elements if they exist. But this breaks
     // how <noscript> is being handled. So we use the same document.
@@ -208,7 +208,7 @@ if (__DEV__) {
           );
     testElement.innerHTML = html;
     return testElement.innerHTML;
-  };
+  }
 }
 
 // HTML parsing normalizes CR and CRLF to LF.

packages/react-dom-bindings/src/client/setInnerHTML.js

@@ -7,24 +7,15 @@
  * @flow
  */
 
+/* globals MSApp */
+
 import {SVG_NAMESPACE} from './DOMNamespaces';
-import createMicrosoftUnsafeLocalFunction from './createMicrosoftUnsafeLocalFunction';
 import {enableTrustedTypesIntegration} from 'shared/ReactFeatureFlags';
 
 // SVG temp container for IE lacking innerHTML
 let reusableSVGContainer: HTMLElement;
 
-/**
- * Set the innerHTML property of a node
- *
- * @param {DOMElement} node
- * @param {string} html
- * @internal
- */
-const setInnerHTML: (
-  node: Element,
-  html: {valueOf(): {toString(): string, ...}, ...},
-) => void = createMicrosoftUnsafeLocalFunction(function (
+function setInnerHTMLImpl(
   node: Element,
   html: {valueOf(): {toString(): string, ...}, ...},
 ): void {
@@ -66,6 +57,26 @@ const setInnerHTML: (
     }
   }
   node.innerHTML = (html: any);
-});
+}
+
+let setInnerHTML: (
+  node: Element,
+  html: {valueOf(): {toString(): string, ...}, ...},
+) => void = setInnerHTMLImpl;
+// $FlowFixMe[cannot-resolve-name]
+if (typeof MSApp !== 'undefined' && MSApp.execUnsafeLocalFunction) {
+  /**
+   * Create a function which has 'unsafe' privileges (required by windows8 apps)
+   */
+  setInnerHTML = function (
+    node: Element,
+    html: {valueOf(): {toString(): string, ...}, ...},
+  ): void {
+    // $FlowFixMe[cannot-resolve-name]
+    return MSApp.execUnsafeLocalFunction(function () {
+      return setInnerHTMLImpl(node, html);
+    });
+  };
+}
 
 export default setInnerHTML;

packages/react-dom-bindings/src/client/setTextContent.js

@@ -18,7 +18,7 @@ import {TEXT_NODE} from './HTMLNodeType';
  * @param {string} text
  * @internal
  */
-const setTextContent = function (node: Element, text: string): void {
+function setTextContent(node: Element, text: string): void {
   if (text) {
     const firstChild = node.firstChild;
 
@@ -32,6 +32,6 @@ const setTextContent = function (node: Element, text: string): void {
     }
   }
   node.textContent = text;
-};
+}
 
 export default setTextContent;