fix(core): TypeScript related migrations should cater for BOM (#30719)

fix(@schematics/angular): TypeScript related migrations should cater for BOM

In the CLI `UpdateRecorder` methods such as `insertLeft`, `remove` etc.. accepts positions which are not offset by a BOM. This is because when a file has a BOM a different recorder will be used https://github.com/angular/angular-cli/blob/master/packages/angular_devkit/schematics/src/tree/recorder.ts#L72 which caters for an addition offset/delta.

The main reason for this is that when a developer is writing a schematic they shouldn't need to compute the offset based if a file has a BOM or not and is handled out of the box.

Example
```ts
recorder.insertLeft(5, 'true');
```

However this is unfortunate in the case if a ts SourceFile is used and one uses `getWidth` and `getStart` method they will already be offset by 1, which at the end it results in a double offset and hence the problem.

Fixes #30713

PR Close #30719

packages/core/schematics/migrations/move-document/index.ts

@@ -48,7 +48,10 @@ function runMoveDocumentMigration(tree: Tree, tsconfigPath: string, basePath: st
   // source files, it can end up updating query definitions multiple times.
   host.readFile = fileName => {
     const buffer = tree.read(relative(basePath, fileName));
-    return buffer ? buffer.toString() : undefined;
+    // Strip BOM as otherwise TSC methods (Ex: getWidth) will return an offset which
+    // which breaks the CLI UpdateRecorder.
+    // See: https://github.com/angular/angular/pull/30719
+    return buffer ? buffer.toString().replace(/^\uFEFF/, '') : undefined;
   };
 
   const program = ts.createProgram(parsed.fileNames, parsed.options, host);