fix: emit source dts files in ts_project output

[jbedard]

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

Source ts_project(srcs) dts files are now passed through to the resulting JsInfo as-is with no modifications or outDir/rootDir applied just like tsc does not emit them while emitted dts may still depend on them.

Test plan

• Covered by existing test cases
• New test cases added

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[jbedard]

Summary:

Consequences match tsc too:

• dist/index.d.ts re-exporting ./types dangles — identical to tsc (verified with both compilers earlier).
• A consumer importing the .d.ts at its source path works — identical to tsc.
• npm_package ships the .d.ts at its source path — same as npm publish with files covering it.

[jbedard]

@acozzette WDYT of this? Technically I think this is "more aligned with tsc", but it sure is odd 🤷

[jbedard]

Where things like .js when allowJson or .json when resolveJsonModule do have rootDir+outDir applied and get fully copied/outputted to bin...

[jbedard]

FWIW I'm trying to make oxc_transpile do similar to what rules_ts/tsc does: aspect-build/rules_oxc#48

[acozzette]

I feel like I'm not familiar enough with the situation to have a very informed opinion. But if the choice is between copying the file and not copying it, doing less for now seems like a good call.

[jbedard]

tsc does not copy it, so I think we should do the same. However outside bazel that original .d.ts in your source is still available - which is where this PR comes in, should the original .d.ts source file be put into the JsInfo.types? That's what this PR adds...

[acozzette]

I think that makes sense. If we're already doing it in the common case where out_dir matches root_dir then it seems reasonable to do that when they're not equal as well.