Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

web_src/js/render/ansi.ts

@@ -0,0 +1,45 @@
+import {AnsiUp} from 'ansi_up';
+
+const replacements = [
+  [/\x1b\[\d+[A-H]/g, ''], // Move cursor, treat them as no-op
+  [/\x1b\[\d?[JK]/g, '\r'], // Erase display/line, treat them as a Carriage Return
+];
+
+// render ANSI to HTML
+export function renderAnsi(line) {
+  // create a fresh ansi_up instance because otherwise previous renders can influence
+  // the output of future renders, because ansi_up is stateful and remembers things like
+  // unclosed opening tags for colors.
+  const ansi_up = new AnsiUp();
+  ansi_up.use_classes = true;
+
+  if (line.endsWith('\r\n')) {
+    line = line.substring(0, line.length - 2);
+  } else if (line.endsWith('\n')) {
+    line = line.substring(0, line.length - 1);
+  }
+
+  if (line.includes('\x1b')) {
+    for (const [regex, replacement] of replacements) {
+      line = line.replace(regex, replacement);
+    }
+  }
+
+  if (!line.includes('\r')) {
+    return ansi_up.ansi_to_html(line);
+  }
+
+  // handle "\rReading...1%\rReading...5%\rReading...100%",
+  // convert it into a multiple-line string: "Reading...1%\nReading...5%\nReading...100%"
+  const lines = [];
+  for (const part of line.split('\r')) {
+    if (part === '') continue;
+    const partHtml = ansi_up.ansi_to_html(part);
+    if (partHtml !== '') {
+      lines.push(partHtml);
+    }
+  }
+
+  // the log message element is with "white-space: break-spaces;", so use "\n" to break lines
+  return lines.join('\n');
+}