Part of #9999.

• Remove AITIP::MergeContextWithCache
• Remove AITIP::CopyContext, AITIP::RestoreContextOnly
• Remove AITIP::QueueAction (see chore(windows): remove WM_KEYMANDEBUG_ messages #10050)
• Remove AIWin2000Unicode::context
• Where context->Reset() is used, instead tell core to reset km_core_state_context_clear
• Move AppContext class to calldll.cpp, and remove from appint.h, and remove unused functionality (as AppContext still used by some of the calldll interactions)
• Remove AIWin2000Unicode::QueueAction
• Remove ContextItemsFromAppContext from appint
• Update AppIntegration::ReadContext() to bool AppIntegration::ReadContext(WCHAR *buf)
• In kmprocess.cpp, ReadContext update: if it returns TRUE, then we will km_core_state_context_set_if_needed