[llvm] [Dexter] Implement DexStepFunction and DexContinue (PR #152721)

[Adrian Prantl via llvm-commits]

adrian-prantl wrote:

> I can't replicate this locally and don't have a way to test arm64. Is there any chance you or someone could run the commands locally that lit spits out, with `--dap-message-log=log.txt` added to the dexter command and pass me that log?
> 
> Something like this:
> 
> ```
> $ clang++ -O0 -glldb -std=gnu++11 <path-to-test>/dex-continue.cpp -o <tmp-dir>/dex-continue.cpp.tmp
> $ python "<path-to-llvm-project>/cross-project-tests/debuginfo-tests/dexter/dexter.py" test --fail-lt 1.0 -w --debugger lldb-dap --lldb-executable "<path-to-llvm-build-dir>/bin/lldb-dap" -v --binary <tmp-dir>/dex-continue.cpp.tmp --dap-message-log=log.txt -- <path-to-test>/dex-continue.cpp
> ```

Ever since we migrated the machines I no longer have ssh access, but I can try to replicate it locally. If that doesn't work, I"m fine with you pushing a commit that temporarily adds more logging to the test case to get the data from the bot.

https://github.com/llvm/llvm-project/pull/152721