refactor(@angular/build): extract shared concurrency, watcher, and styling utilities

[alan-agius4]

Extract shared utilities from the application builder so they can be reused across builders:

• Extract runConcurrent and mapConcurrent into utils/concurrency.ts
• Extract setupWatcher into tools/esbuild/watcher.ts
• Extract getTailwindConfig into utils/postcss-configuration.ts
• Update stylesheet bundling options and CSS resource plugin to support data URLs
• Expose resolvePath on BuilderHarness

[gemini-code-assist]

Code Review

This pull request introduces several refactorings and new features, including the extraction of file watcher setup logic into a reusable setupWatcher helper, the addition of a dataurl option to inline stylesheet resources as base64 data URIs, and the introduction of new concurrency utilities (runConcurrent and mapConcurrent) to handle limited-concurrency asynchronous operations. Additionally, the getTailwindConfig helper was moved to postcss-configuration.ts. Feedback on these changes highlights a potential memory leak in setupWatcher where the 'abort' event listener registered on the AbortSignal is not removed when the watcher is closed.