[lldb][test] Add mock GPU DAP test for startDebugging reverse request

[thechenli]

Summary

Add a DAP test for the mock GPU plugin that verifies the startDebugging reverse request is sent with the correct structure when a mock GPU target is created. This mirrors the AMD GPU DAP test from #72 but uses the mock GPU plugin, allowing the test to run in CI on any machine without real GPU hardware.

The test validates:

• The reverse request command is startDebugging with request type attach
• The session name is "Mock GPU Session"
• The configuration includes valid debuggerId and targetId fields
• The test correctly handles multiple GPU plugins being active simultaneously by filtering for the mock GPU session name

Files added

• lldb/test/API/tools/lldb-dap/gpu/mock/TestDAP_mock_gpu_reverse_request.py — test
• lldb/test/API/tools/lldb-dap/gpu/mock/hello_world.cpp — test program with mock GPU lifecycle functions
• lldb/test/API/tools/lldb-dap/gpu/mock/Makefile — build rules
• lldb/test/API/tools/lldb-dap/gpu/mock/lit.local.cfg — requires lldb-mock-gpu plugin

Test plan

• Built with -DLLDB_ENABLE_MOCK_GPU_PLUGIN=ON -DLLDB_ENABLE_AMDGPU_PLUGIN=ON
• Ran llvm-lit lldb/test/API/tools/lldb-dap/gpu/mock/ — all tests pass

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[qxy11]

Can this mock more than just the startDebugging request? We should try to send DAP requests to the CPU and mock GPU targets.

[thechenli]

Can this mock more than just the startDebugging request? We should try to send DAP requests to the CPU and mock GPU targets.

yeah, added another test test_dap_requests_to_cpu_and_gpu_targets which hopefully have the e2e testing flow.

[qxy11]

Can we test more than simple commands like stack trace - maybe try continuing to the next mock GPU breakpoint, and CPU breakpoints?

[thechenli]

fyi - the current PR have two CPU breakpoints and only one GPU breakpoint, I am trying to figure out a deadlock issue with multiple GPU breakpoints.

[thechenli]

updated with setting instruction breakpoints for GPU and continue to the breakpoint.