[lldb][test] Add embedded Swift test category

[Teemperor]

This adds a embedded Swift test variant that automatically re-runs test in embedded Swift mode unless
a test explicitly disables this behaviour. It also adds the required skipIfEmbeddedSwift to disable any tests
that currently do not work in embedded Swift. This patch does not yet remove any potentially redundant embedded Swift tests.

How many tests have a passing embedded Swift variant?

About 33% (200) of the 584 Swift tests (1 test = 1 test_* method) pass with embedded Swift. It's hard to automatically classify the remaining failures but they range from LLDB crashing, to linker failures, to unavailable language features in embedded.

I skipped everything without an explicit root cause attached for most tests. So for now a skip decorator that does not have a root-cause attached should be considered a potential bug.

By how much does the test suite runtime increase?

On my M4 Pro machine with 14 logical cores I get the following test timing increases:

• When running all tests total testing time increases from 13:54 -> 14:45 (+6%)
• When running only Swift tests the total test time increases from 7:49 to 8:56 (+16%)

It should be noted that we could now also remove several embedded/ tests so the actual test overhead of this could be lower than listed above. If we (optimistically) removed all potentially redundant embedded Swift tests we would save about 15 seconds of testing time. The numbers above change roughly to +4%/+10% test suite runtime overhead.

[Teemperor]

@swift-ci please test

[Teemperor]

@swift-ci please test

[Teemperor]

Closing in favour of the new #12926