Added returning of original path from Bun.build

[BjornTheProgrammer]

What does this PR do?

This PR fixes #15033, by adding the sourcefile attribute on BuildArtificat. It remains as null if the output is not an entry-point

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

I ran bun-debug test bundle
I added a test to check for the sourcefile attribute, and added onto some tests to do the same.

• I checked the lifetime of memory allocated to verify it's (1) freed and (2) only freed when it should be

• I included a test for the new code, or an existing test covers it

• JSValue used outside outside of the stack is either wrapped in a JSC.Strong or is JSValueProtect'ed

• I wrote TypeScript/JavaScript tests and they pass locally (bun-debug test test-file-name.test)

• I added TypeScript types for the new methods, getters, or setters

[BjornTheProgrammer]

Some things maybe should be considered, such as whether chunks should also have a sourcefile if they existed. Additionally, this code makes it so that sourcefile doesn't display if the type isn't an entry-point. Maybe that should be changed.

[paperdave]

implementation looks reasonable. i want to get other people's opinions on the field name sourcefile. maybe it should be named entrypoint, since it is the pre-resolved text and not the actual path to the file that it built.

[BjornTheProgrammer]

Thanks for the feedback, I've changed it to be entrypoint!

[BjornTheProgrammer]

I've rebased and reran bun-debug test bundler. All tests seem to be passing on my machine.