Fixes#10458.
Refactors the LDML keyboard test window significantly, in order to be
able to support markers. Cleans up the state machine for the debug
window in the process, as that was complicating the changes. Removes
a lot of extraneous code in the debug window.
Relates to #10416.
Moves from using action queue to action struct for the LDML keyboard
debugger. Does not do the same for the KMX keyboard debugger, because
that relies on action items to do single-step debugging.
Fixes#10431.
The `km_core_` prefix has been removed from internal-only functions, and
these function declarations moved to context.hpp.
The functions have not been moved from km_core_context_api.cpp at this
stage.
Rewrote the function documentation in Javadoc style comments for the
internal use functions.
Fixes#7649.
emit_keystroke code path in kmx processor was writing directly to the
core queue instead of to the internal kmx processor queue. This caused
it to be out-of-order in the actions sent to the engine/debugger.
Engines didn't really care but it broke the debugger, for example if
only a deadkey was in the buffer and backspace was pressed, Developer
would assert as it would get unexpected context for the deletions.
