TestFoundation: excise tests that use private APIs

[compnerd]

Since we do not expose the CoreFoundation APIs fully these tests are not
possible to build since the symbols cannot be resolved. Rather than
adding additional exports to CoreFoundation for testing only, just drop
the tests.

[compnerd]

@millenomi - was this the solution that you preferred rather than having a new macro to expose the functions?

[spevans]

Could internal methods be added to wrap these then testing enabled inside NS_FOUNDATION_ALLOWS_TESTABLE_IMPORT blocks? I don't like the idea of disabling so many tests

[millenomi]

We're not disabling tests on platforms where they can run.

I'm okay wrapping these in a SPI file in Foundation that is marked for testing only, as API importable via @testable import or similar. Or disabling them on Windows. But not disabling them tout court.

[millenomi]

Or: use @_cdecl to pull in strictly SPI we need in the test target.

[compnerd]

Using @_cdecl wont work, since the symbols are not available through Foundation.dll. Wrapping them in an SPI is probably nicer.

[compnerd]

The only test which needed to be removed is handled elsewhere. The issues that this was tracking are no longer a problem.