feat(browser): add LoaderSentry type

[faizansaiyed123]

Summary

Adds an exported LoaderSentry type for TypeScript users of the CDN loader.

Changes

• Adds and exports LoaderSentry.
• Represents the APIs supported by the loader stub.
• Uses void return types for queued methods to match the loader's runtime behavior.
• Adds type tests covering supported and unsupported APIs.

This is a TypeScript-only solution and does not change the loader runtime behavior or expand the loader's queued method list.

Related to #21806.

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[faizansaiyed123]

Hi @Lms24, thanks for approving the TypeScript-only approach on #21806.

I've opened #25357, added the focused type tests, and addressed the BugBot feedback. The latest BugBot review found no issues, and the focused type tests pass locally.

The GitHub Actions workflows appear to be awaiting approval for this fork PR. Could you or another maintainer approve them so CI can run?

Thanks for your time!