Refactor Build All OSX tests to reduce redundant data entry.

[sdmaclea]

The Build All tests on OSX feature introduced by #35783, has some rough edges.

Tests are currently disabled in two places.

• <CLRTestUnsupported Condition="...">true<CLRTestUnsupported />
• <ExcludeList Include="<test path>"><Issue>Reason</Issue></ExcludeList>

The duplicate data entry is error prone.

It also confuses

• "runtime issues" and "test bugs"
• "known test limitations" and "known runtime limitations"

The original design also had two disable mechanisms:

• <DisableProjectTestBuild Condition="...">true<DisableProjectTestBuild />
• <TestUnsupportedOutsideWindows/>

This legacy mechanism was designed for when the tests were built on WIndows to be run elsewhere.

[sdmaclea]

Fixed by #36482