[lldb] Fill Watch/AppleTV simulator gaps in PlatformDarwin

When running the test suite against the Watch/AppleTV simulator we currently hitting
the unimplemented parts of PlatformDarwin for the respective simulator platforms.

This just adds the respective switch cases.

This whole code path depends on having a valid Target, so can't just unittest this code
without refactoring it. So instead this is tested by just running the testsuite against
the respective simulators (which is how I found this).

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D89106