[lldb][Windows] Fix TestLocateModuleCallback

D153735 added the tests but it is failing due to POSIX path vs Windows path.
https://lab.llvm.org/buildbot/#/builders/219/builds/4084

Fix it.
- MODULE_PLATFORM_PATH is POSIX path.
- Normalize self.input_dir, FileSpec and SymbolFileSpec fullpath.

Differential Revision: https://reviews.llvm.org/D155124