Run PAL tests in CI (#42049)

Run PAL tests in CI (#42049)

Refactor the PAL test framework to be useable in our CI system, and enable it for testing

The existing PAL tests are problematic in a few ways for our CI.
1. They are large in terms of disk space used per test, this interferes with building them properly, especially as they are part of the product build, and not of the test build
2. While part of the product build, the option to build them was well hidden.
3. The tests are not related to our existing tests, and in particular are not driven from managed xunit wrappers.

The change here has 4 components
1. Reduce the volume of the binaries such that they can be passed from a product build to a test job effectively. This is done by merging all tests which are not strictly dependent on secondary libraries.
  - This was done via a tool which parsed and replaced all of the CMakeFiles.txt
  - And then manual editing to remove all duplicate global symbols
2. The build flag for building the tests has been exposed as a first class option to build-runtime, as well as through the subset mechanism. As of this change, developers who wish to build the tests should use the clr.paltests subset to build the tests.
3. As the tests do not have normal xunit wrappers, but they *do* have a script which will generate xunit output, they cannot quite be run in the existing helix pathway. Add a separate path for launch the appropriate helix workitem as part of outerloop test runs.
4. A new issue exclusion mechanism has been built. Add exclusions by modifying src/coreclr/src/pal/tests/palsuite/issues.targets
  - There are a number of failures in the current test suite that should probably be investigated, but making meaningful changes to the tests should not be part of this change.