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!

[Lms24]

I made some changes to this PR to get it passing with our lint rules and also make the type imports and exports a bit simpler.

• Replaced typeof import() with named import type statements, because the repo's lint rule bans import() type annotations.
• Replaced the mapped type with an explicit LoaderSentry interface that lists each safe method.
• withScope now only takes the single-callback form, so withScope(scope => …) type-checks. in the loader you can't really pass a scope to withScope
• Added a JSDoc usage example to LoaderSentry, including that when LoaderSentry is declared via global, a type cast needs to happen in Sentry.onLoad where all APIs can be accessed safely and have their original signature again.
• Renamed src/loader.ts to src/loader-types.ts so it doesn't look like loader runtime code.
• Added type tests that check method parameters and the withScope signature.
• Deleted tsconfig.loader.test.json and pointed typecheck at the shared tsconfig.test.json, as packages/cloudflare does.
• Added ignoreSourceErrors: true, because 37 type errors already in other browser test files would otherwise fail the run.
• Formatting

[Lms24]

Thanks for contributing!