Add `stop_description` as a Python convenience property to `SBThread`.

This is only implemented for x86.
Originally introduced in: https://github.com/llvm/llvm-project/pull/137904

Expose `QueueThreadPlanForStepSingleInstruction` function to
SBThreadPlan

This reverts commit a2e3af5d581547d3ea53e5383d6f7f1cab45120a and solves
the build error in
https://lab.llvm.org/buildbot/#/builders/141/builds/369.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

This reverts commit 1130e923e2d7fe046101bf639bc5ebcde194c005.
Very likely causes build problems on Windows and with LLVM_NO_DEAD_STRIP=ON,
see https://github.com/llvm/llvm-project/pull/96985#pullrequestreview-2147599208

This patch changes `ScriptedThreadPlan::GetStopDescription` behavior by
discarding its return value since it is optional in the first place (the
user doesn't need to provide a return value in their implementation).

This patch also addresses the test failures in TestStepScripted
following 9a9ec22 and re-enables the tests that were XFAIL'd previously.

The issue here was that the `Stream*` that's passed to
`ThreadPlanPython::GetDescription` wasn't being passed by reference to
the python method so it was never updated to reflect how the python
method interacted with it.

This patch solves this issue by making a temporary `StreamSP` that will
be passed to the python method by reference, after what we will copy its
content to the caller `Stream` pointer argument.

---------

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

Reverts llvm/llvm-project#96942 since the test failures are still
happening:

https://lab.llvm.org/buildbot/#/builders/162/builds/899/

This tentatively reverts commit 204c403b5215197ecdbdb68ca7f11402d6d9892b
to remove the XFAIL from the tests while also trying to fix them at the
same time.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

XFAIL in #96894 was too wide. This one actually passes.