Fix mermaid-related bugs (#21431)

web_src/js/bootstrap.js

@@ -25,6 +25,10 @@ function processWindowErrorEvent(e) {
     // If a script inserts a newly created (and content changed) element into DOM, there will be a nonsense error event reporting: Script error: line 0, col 0.
     return; // ignore such nonsense error event
   }
+
+  // Wait for upstream fix: https://github.com/microsoft/monaco-editor/issues/2962
+  if (e.message.includes('Language id "vs.editor.nullLanguage" is not configured nor known')) return;
+
   showGlobalErrorMessage(`JavaScript error: ${e.message} (${e.filename} @ ${e.lineno}:${e.colno}). Open browser console to see more details.`);
 }
 

web_src/js/markup/mermaid.js

@@ -50,7 +50,7 @@ export async function renderMermaid() {
       // can't use bindFunctions here because we can't cross the iframe boundary. This
       // means js-based interactions won't work but they aren't intended to work either
       mermaid.mermaidAPI.render('mermaid', source, (svgStr) => {
-        const heightStr = (svgStr.match(/height="(.+?)"/) || [])[1];
+        const heightStr = (svgStr.match(/viewBox="(.+?)"/) || ['', ''])[1].split(/\s+/)[3];
         if (!heightStr) return displayError(el, new Error('Could not determine chart height'));
         const iframe = document.createElement('iframe');
         iframe.classList.add('markup-render');