Add clang_CXXMethod_isMoveAssignmentOperator to libclang

Add clang_CXXMethod_isMoveAssignmentOperator to libclang

The new method is a wrapper of `CXXMethodDecl::isMoveAssignmentOperator` and
can be used to recognized move-assignment operators in libclang.

An export for the function, together with its documentation, was added to
"clang/include/clang-c/Index.h" with an implementation provided in
"clang/tools/libclang/CIndex.cpp". The implementation was based on
similar `clang_CXXMethod.*` implementations, following the same
structure but calling `CXXMethodDecl::isMoveAssignmentOperator` for its
main logic.

The new symbol was further added to "clang/tools/libclang/libclang.map"
to be exported, under the LLVM16 tag.

"clang/tools/c-index-test/c-index-test.c" was modified to print a
specific tag, "(move-assignment operator)", for cursors that are
recognized by `clang_CXXMethod_isMoveAssignmentOperator`.
A new regression test file,
"clang/test/Index/move-assignment-operator.cpp", was added to ensure
whether the correct constructs were recognized or not by the new function.

The "clang/test/Index/get-cursor.cpp" regression test file was updated
as it was affected by the new "(move-assignment operator)" tag.

A binding for the new function was added to libclang's python's
bindings, in "clang/bindings/python/clang/cindex.py", adding a new
method for `Cursor`, `is_move_assignment_operator_method`.
An accompanying test was added to
`clang/bindings/python/tests/cindex/test_cursor.py`, testing the new
function with the same methodology as the corresponding libclang test.

The current release note, `clang/docs/ReleaseNotes.rst`, was modified to
report the new addition under the "libclang" section.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D137246