[lldb][PlatformDarwin] Make LocateExecutableScriptingResourcesFromDSYM a public static (#185056)
This will allow us to unit-test it in a follow-up patch. We could test
`LocateExecutableScriptingResources` directly, but that requires a valid
`Module`/`ObjectFile`/`SymbolFile`. That's a lot of boilerplate/set to
ultimately just test the `dSYM` logic. The helper just takes
`FileSpec`s, which are much easier to construct in a test.