[lldb][LocateModuleCallback] Call locate module callback

RFC https://discourse.llvm.org/t/rfc-python-callback-for-target-get-module/71580

Updated Target::GetOrCreateModule to call locate module callback if set.

- include/lldb/Target/Platform.h, source/Target/Platform.cpp
  - Implemented SetLocateModuleCallback and GetLocateModuleCallback*

- include/lldb/Target/Target.h, source/Target/Target.cpp
  - Implemented CallLocateModuleCallbackIfSet.

- unittests/Target/LocateModuleCallbackTest.cpp
  - Added comprehensive GetOrCreateModule tests.

Differential Revision: https://reviews.llvm.org/D153734