[lldb] [llvm] [lldb-dap] Add unknown request handler (PR #181109)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64le-flang-rhel-clang` running on `ppc64le-flang-rhel-test` while building `lldb,llvm` at step 7 "test-build-unified-tree-check-flang-rt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/157/builds/44481

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-build-unified-tree-check-flang-rt) failure: 1200 seconds without output running [b'ninja', b'check-flang-rt'], attempting to kill
...
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/219/253 (244 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/210/253 (245 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/209/253 (246 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/220/253 (247 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/221/253 (248 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/215/253 (249 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/226/253 (250 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/24/253 (251 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/218/253 (252 of 258)
PASS: flang-rt-Unit :: Runtime/./RuntimeTests/72/253 (253 of 258)
command timed out: 1200 seconds without output running [b'ninja', b'check-flang-rt'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2562.456688

```

</details>

https://github.com/llvm/llvm-project/pull/181109