This patch introduces a new scripting affordance in lldb:
`ScriptedFrame`.

This allows user to produce mock stackframes in scripted threads and
scripted processes from a python script.

With this change, StackFrame can be synthetized from different sources:
- Either from a dictionary containing a load address, and a frame index,
  which is the legacy way.
- Or by creating a ScriptedFrame python object.

One particularity of synthezising stackframes from the ScriptedFrame
python object, is that these frame have an optional PC, meaning that
they don't have a report a valid PC and they can act as shells that just
contain static information, like the frame function name, the list of
variables or registers, etc. It can also provide a symbol context.

rdar://157260006

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

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

The current implementation tries to (1) patch the existing readline
module definition if it's already present in the inittab and (2) append
our patched readline module to the inittab. The former (1) uses the
non-stable Python API and I can't find a situation where this is
necessary. 

We do this work before initialization, so for the readline
module to exist, it either needs to be added by Python itself (which
doesn't seem to be the case), or someone would have had to have added it
without initializing.

Use `PyThread_get_thread_ident`, which is part of the Stable API,
instead of accessing a member of the PyThreadState, which is opaque when
using the Stable API.

PyConfig and friends are not part of the stable API. We could switch
back to Py_SetPythonHome, which has been deprecated, but still part of
the stable API. For now, limit the use of PyConfig to when
LLDB_EMBED_PYTHON_HOME is enabled, which essentially means Windows.
Changing the order doesn't seem to matter.

Eliminate calls to PyGILState_Check, which is not part of the Python
Limited C API. In the Locker, we can use PyGILState_Ensure directly. We
could do something similar to replace the assert, but I don't think it's
worth it. We don't assert that we hold the GIL anywhere else.

Eliminate the `log` variable by inlining the GetLog call and use
"locked" and "unlocked" directly, as requested by Ismail in #151780.

The behavior of thread initialization changed in Python 3.7. The minimum
supported Python version is now 3.8. That means that
`PyEval_ThreadsInitialized` always returns true and `PyEval_InitThreads`
is never called.

The helper function existed to coordinate initializing the threads and
acquiring the GIL, which is no longer necessary. With that, there's no
point in having the helper at all. This PR eliminates the function and
inlines to GIL acquisition into the caller.

Reimplment `PyRun_SimpleString` using the Python stable C API and the
`RunString` helper.

Part of https://github.com/llvm/llvm-project/issues/151617

This is NFC, I'm modernizing the interface before I add to it in a
subsequent commit.

This is a continuation of 68fd102, which did the same thing but only for
StopInfo. Using make_shared is both safer and more efficient:

- With make_shared, the object and the control block are allocated
  together, which is more efficient.
- With make_shared, the enable_shared_from_this base class is properly
  linked to the control block before the constructor finishes, so
  shared_from_this() will be safe to use (though still not recommended
  during construction).