[lldb][NFC] Move non-clang specific method to the generic DWARF Parser

This patch renames DW_ACCESS_to_AccessType function and move it to the abstract
DWARFASTParser, since there is no clang-specific code there. This is useful for
plugins other than Clang.

Reviewed By: shafik, bulbazord

Differential Revision: https://reviews.llvm.org/D114719