fix(@angular/build): show clear error when styleUrl points to a TypeScript file

[maruthang]

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix

What is the current behavior?

When a component's styleUrl accidentally points to a .ts file instead of a stylesheet, confusing downstream errors appear (e.g., rxjs-related errors) that don't indicate the actual problem.

Issue Number: #32193

What is the new behavior?

TypeScript files (.ts, .tsx, .mts, .cts) used as component resources are now rejected early in the Angular compiler host, producing a clear "Could not find stylesheet file" error message that points to the actual problem.

Does this PR introduce a breaking change?

• Yes
• No

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[gemini-code-assist]

Code Review

This pull request prevents TypeScript files from being incorrectly processed as component resources by the Angular compiler host, which avoids confusing downstream errors. The changes include a new validation check in the compiler host and a test case to ensure that using a TypeScript file in styleUrl triggers an error. Feedback suggests refactoring the hasTypeScriptExtension helper function to use Array.includes() for improved conciseness.

[gemini-code-assist]

For improved readability and conciseness, you could use an array with includes() to check for the file extension. This avoids the more verbose switch statement.

function hasTypeScriptExtension(file: string): boolean {
  const extension = nodePath.extname(file).toLowerCase();

  return ['.ts', '.tsx', '.mts', '.cts'].includes(extension);
}