test: Expand coverage of sourcemap validator (#25115)

<!--
Please submit this PR as a draft initially.
Do not mark it as "Ready for review" until the template has been
completely filled out, and PR status checks have passed at least once.
-->

## **Description**

The sourcemap validator script has been updated to cover all build
files. This better protects against sourcemap errors.

The file `offscreen-0.js` is optionally validated. It is expected to be
missing in MV2 builds.

One file is still skipped because validation is failing
(`sentry-install.js`).

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/25115?quickstart=1)

## **Related issues**

N/A

## **Manual testing steps**

* Run `yarn dist`
* Run `yarn validate-source-maps`, and see that it succeeds.

## **Screenshots/Recordings**

N/A

## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

development/sourcemap-validator.js

@@ -22,25 +22,38 @@ start().catch((error) => {
 
 async function start() {
   const targetFiles = [
-    `common-0.js`,
-    `background-0.js`,
-    `ui-0.js`,
-    `scripts/contentscript.js`,
-    // `scripts/inpage.js`, skipped because the validator can't sample the inlined `scripts/inpage.js` script
+    'background-0.js',
+    'common-0.js',
+    'content-script-0.js',
+    'ui-0.js',
+    'scripts/contentscript.js',
+    'scripts/disable-console.js',
+    'scripts/policy-load.js',
+    // TODO: Investigate why these are failing
+    // 'scripts/sentry-install.js',
+    // `scripts/inpage.js`,
   ];
+  const optionalTargetFiles = ['scripts/app-init.js', 'offscreen-0.js'];
   let valid = true;
 
   for (const buildName of targetFiles) {
     const fileIsValid = await validateSourcemapForFile({ buildName });
     valid = valid && fileIsValid;
   }
+  for (const buildName of optionalTargetFiles) {
+    const fileIsValid = await validateSourcemapForFile({
+      buildName,
+      optional: true,
+    });
+    valid = valid && fileIsValid;
+  }
 
   if (!valid) {
     process.exit(1);
   }
 }
 
-async function validateSourcemapForFile({ buildName }) {
+async function validateSourcemapForFile({ buildName, optional = false }) {
   console.log(`build "${buildName}"`);
   const platform = `chrome`;
   // load build and sourcemaps
@@ -56,6 +69,12 @@ async function validateSourcemapForFile({ buildName }) {
     // empty
   }
   if (!rawBuild) {
+    if (optional) {
+      console.warn(
+        `SourcemapValidator - file not found, skipping "${buildName}"`,
+      );
+      return true;
+    }
     throw new Error(
       `SourcemapValidator - failed to load source file for "${buildName}"`,
     );