[lldb] Allow configuring on Windows with python interpreter within a junction

[lldb] Allow configuring on Windows with python interpreter within a junction

The current implementation nicely takes into account when the python interpreter is symlinked (or transitively within a symlinked directory). Sadly, `os.path.islink` returns `false` on Windows if instead of Windows symlinks, junctions are used. This has caused me issues after I started using `scoop` as my package manager on Windows, which creates junctions instead of symlinks.
The fix proposed in this patch is to check whether `realpath` returns a different path to `exe`, and if it does, to simply try again with that path.
The code could also be simplified since `sys.executable` is guaranteed to be absolute, and `os.readlink`, which can return a relative path, is no longer used.

Tested on Windows 11 with Python 3.11 as interpreter and Ubuntu 18.04 with Python 3.6

Differential Revision: https://reviews.llvm.org/D141042