The core no longer cares which thread is the host thread.

Cleaning up Android's HostThreadLock is left for another PR, in part
because the HostThreadLock in NativeConfig.cpp still serves a purpose,
and in part to make any issues easier to bisect.

Remove Host_RefreshDSPDebuggerWindow (which hasn't done anything since
DolphinWX was removed in 44b22c90) and DSP::Host::UpdateDebugger (which
only called Host_RefreshDSPDebuggerWindow).

Remove Host_UpdateMainFrame(). The only non-empty call happened in
DolphinNoGUI which called s_update_main_frame_event.Set(), but
DolphinNoGUI never waits on that event.

DolphinTool: Make variables constant

Using the `-Wnrvo` flag introduced by GCC 14, I identified a few places where NRVO was clearly intended, but is fumbled.