[wip] Load type infos correctly

[blizzy78]

This PR changes the loading of type infos in GoSourceFile.Incubate such that mutation tests should no longer fail, a bug that had been introduced in #5. With this PR, all tests and mutation tests seem to run fine for me.

I did have to explicitly disable ooze_test.TestOoze_nothing_to_test and ooze_test.TestOoze_with_mutations. These tests do not use regular Go source files on disk, but rather in-memory source "files". Perhaps these should be changed to regular files.
This PR is still a work in progress because of those disabled tests.

I have removed go:build testdata flags from all Go source files in testdata folders. For one, they don't seem to be necessary at all, and two, they prevent this PR from working.

This PR supersedes #10.

[blizzy78]

@gtramontina Do you have thoughts about the disabled tests?

[gtramontina]

Thanks for putting in the hard work, @blizzy78! 🙏

@gtramontina Do you have thoughts about the disabled tests?

It seems that the ooze_test.TestOoze_nothing_to_test tests pass, but seeminly for the wrong reason. 🤔

Having the mutation tests running is a testment of the fix, although I'd like to have some level of coverage on internal/ooze/ooze.go. Perhaps, as you said, by using regular on-disk files, or even explore packagetest, as it seems that the package package reads the actual file system.

I'm happy to move forward with these tests skipped for now, but I'll likely come back to them soon.

[gtramontina]

Will this ever happen? I'm thinking that if it ever happens, it means that something has actually gone wrong pretty badly, no? I'd consider blowing up with a panic here. WDYT?

[blizzy78]

Yeah sounds good to me.

[blizzy78]

I didn't know package packagestest existed. This certainly looks interesting. I can try converting the disabled tests to using that.