lib: add UNC support to url.pathToFileURL()

[mceachen]

Fixes: #34736

Checklist

• make -j4 test (UNIX) passes
• vcbuild test (Windows) passes
• tests are included
• commit message follows commit guidelines
• certified Developer's Certificate of Origin 1.1

[guybedford]

This looks great to me, thank you so much @mceachen for the PR.

Let's get a review from @jasnell as well to land.

[mceachen]

Seems like test-asan failed from something not related to this PR:

=== release test ===
Path: node-api/test_worker_terminate_finalization/test
##[error]--- stderr ---
=================================================================
==107572==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 80 byte(s) in 1 object(s) allocated from:
    #0 0xa1d80d in operator new(unsigned long) (/home/runner/work/node/node/out/Release/node+0xa1d80d)
    #1 0xb5bf63 in napi_create_reference (/home/runner/work/node/node/out/Release/node+0xb5bf63)
    #2 0x7f5a275d1878  (<unknown module>)
    #3 0xb47492 in v8impl::(anonymous namespace)::FunctionCallbackWrapper::Invoke(v8::FunctionCallbackInfo<v8::Value> const&) (/home/runner/work/node/node/out/Release/node+0xb47492)
    #4 0x1268a73 in v8::internal::FunctionCallbackArguments::Call(v8::internal::CallHandlerInfo) (/home/runner/work/node/node/out/Release/node+0x1268a73)
    #5 0x12668a4 in v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) (/home/runner/work/node/node/out/Release/node+0x12668a4)
    #6 0x1264932 in v8::internal::Builtin_Impl_HandleApiCall(v8::internal::BuiltinArguments, v8::internal::Isolate*) (/home/runner/work/node/node/out/Release/node+0x1264932)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32742/ (💚)

[jasnell]

@mceachen ... yeah, that's a known issue. A fix is pending.

[lpinca]

Suggested change

	// In posix, "/" is a valid character in paths
	// In posix, "\" is a valid character in paths

[mceachen]

Ah, good catch. I just moved this comment, btw, when I refactored out the function. Will fix.

[mceachen]

Thanks for the reviews! Is there anything else I need to do for this PR? (I haven't committed to this project before).

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32772/

[Trott]

Landed in 7b8c6b0.

Thanks for the contribution! 🎉