[LLDB] Update inspect getargspec to getfullargspec

This patch replaces getargspec with getfullargspec in funcutils.py.
getargspec has been deprecated by python 11x release. This is
important to run LLDB testsuite in Windows/Arm64 platform
where Python native will be available from python release onwards.

Note: getfullargspec is not available in python 2

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D121786