Fix mermaid related bugs

1. Apparently, mermaid 9.1.7 no longer sets a `height` attribute on the
   SVG it produces. Workaround by extracting height from `viewBox`
   instead.
2. Filter out unresolvable Monaco errors from error display.

Fixes: go-gitea#21427
Ref: microsoft/monaco-editor#2962

web_src/js/bootstrap.js

@@ -7,9 +7,18 @@ import {joinPaths} from './utils.js';
 // This file must be imported before any lazy-loading is being attempted.
 __webpack_public_path__ = joinPaths(window?.config?.assetUrlPrefix ?? '/', '/');
 
+const ignoreErrors = [
+  /vs\.editor\.nullLanguage/, // https://github.com/microsoft/monaco-editor/issues/2962
+];
+
 export function showGlobalErrorMessage(msg) {
   const pageContent = document.querySelector('.page-content');
   if (!pageContent) return;
+
+  for (const re of ignoreErrors) {
+    if (re.test(msg)) return;
+  }
+
   const el = document.createElement('div');
   el.innerHTML = `<div class="ui container negative message center aligned js-global-error" style="white-space: pre-line;"></div>`;
   el.childNodes[0].textContent = msg;

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');