chore(jest-transform): refactor transformer API to reduce number of arguments

docs/CodeTransformation.md

@@ -23,6 +23,12 @@ You can write you own transformer. The API of a transformer is as follows:
 
 ```ts
 interface Transformer {
+  /**
+   * Indicates if the transformer is capabale of instrumenting the code for code coverage.
+   *
+   * If V8 coverage is _not_ active, and this is `true`, Jest will assume the code is instrumented.
+   * If this is `false` Jets will instrument the code returned by this transformer using Babel. 
+   */
   canInstrument?: boolean;
   createTransformer?: (options?: unknown) => Transformer;
 
@@ -59,7 +65,9 @@ type TransformedSource =
 // RawSourceMap comes from [`source-map`](https://github.com/mozilla/source-map/blob/0.6.1/source-map.d.ts#L6-L12)
 ```
 
-As can be seen, only `process` is mandatory to implement, although we highly recommend implementing `getCacheKey` as well, so we don't waste resources transpiling the same source file when we can read its previous result from disk.
+As can be seen, only `process` is mandatory to implement, although we highly recommend implementing `getCacheKey` as well, so we don't waste resources transpiling the same source file when we can read its previous result from disk. You can use [`@jest/create-cache-key-function`](https://www.npmjs.com/package/@jest/create-cache-key-function) to help implement it.
+
+Note that [ECMAScript module](ECMAScriptModules.md) support is indicated by the passed in `supports*` options. Specifically `supportsDynamicImport: true` means the transformer can return `import()` expressions, which is supported by both ESM and CJS. If `supportsStaticESM: true` it means top level `import` statements are supported and the code will be interpreted as ESM and not CJS. See [Node's docs](https://nodejs.org/api/esm.html#esm_differences_between_es_modules_and_commonjs) for details on the differences.
 
 ### Examples