docs: add jsdoc instead of comments

[alan-agius4]

This changes was originally required for the API guardian as it was not liking the comments as they were. But I am going to land it separately.

• Use jsdocs / tsdocs instead of comments
• rename file from .d.ts to .ts. This is due that d.ts don't get typechecked because we have skipLibCheck enabled which might result in invalid declarations. Referenced dts files don’t get emitted by tsc, which means there should be a separate build process to copy this dts file to dist. And finally I'd very much like to avoid issues like this Cannot find name 'FileReplacements'. #11294 just because we use d.ts instead of .ts

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