Filter out non-header files from Compile Source phase

[maxwellE]

Fixes #414.

[brentleyjones]

Looks like you need to update the fixtures: https://github.com/buildbuddy-io/rules_xcodeproj/blob/main/CONTRIBUTING.md#developing

[brentleyjones]

Some changes are needed in Fixtures.swift. You should be able to run the tests locally with bazel test --config=cache //tools/....

[tinder-maxwellelliott]

Some changes are needed in Fixtures.swift. You should be able to run the tests locally with bazel test --config=cache //tools/....

On it now

[maxwellE]

Some changes are needed in Fixtures.swift. You should be able to run the tests locally with bazel test --config=cache //tools/....

@brentleyjones How do you debug these AssertNoDifferences, I only get a subset of the change and I cannot easily tell which target owns the added PBXObjectReference

[brentleyjones]

Yeah, sometimes the diffs hide context. For these though, you know you are removing files from the Compile Sources, so you'll need to remove things from PBXSourcesBuildPhase initializers (or the phases all together) for targets that had headers there. One example is PBXBuildFile(file: elements["z.h"]!),.