[lldb] Workaround omission of PyBUF_READ in the stable API (#152214)

PyMemoryView_FromMemory is part of stable ABI but the flag constants
such as PyBUF_READ are not. This was fixed in Python 3.11 [1], but still
requires this workaround when using older versions.

[1] https://github.com/python/cpython/issues/98680

GitOrigin-RevId: 7b8dea265e72c3037b6b1e54d5ab51b7e14f328b