Removes a lot of unused functions and one unit. Cleanup for debugging.

Refactors visual keyboard import from kmx to use Keyman Core, and at the
same time removes any UI interactions or direct Windows dependencies
from the process.

Start of the refactor of the debugger to use Keyman Core. Basic events
work but there is a lot to tidy up yet.

Moves the responsibility for deletion of markers when the users presses
the backspace key, from `kmx_processor::process_event` to
`KMX_ProcessEvent::ProcessGroup`. This has no effect on usage of Keyman
Core, but:

1. Simplifies the association between context and action further
2. Ensures that `m_actions` and `state->actions` will always be the
   same length, making future refactoring of these simpler
3. Allows us to use the index into the m_actions array for Debug events,
   which simplifies the interleaving of these for the upcoming Debugger.

When the user presses backspace at start of context (where there may be
markers in the cached context, but no characters), the kmx processor
will delete any markers prior to insertion point before requesting that
the consumer emit the backspace virtual key back to the application, to
allow the application to handle backspace at start of text.

Per review comments.

Merge branch 'chore/common/core/debug-additional-tests' into chore/common/core/5488-delete-markers-reliably

Also introduce a specific enum for backspace type rather than
inappropriately using the action item type enum.

Fixes #5488.

This updates Keyman Core, corresponding tests, and Keyman Engine for
Linux to support deletion of markers through an action, ensuring that
the action queue does not desynchronize with the context.

auto: increment master version to 15.0.89

chore(common/core): Implement capsAlwaysOff system store 🚧

This change implements the core part in a way that makes the tests
pass. This still needs corresponding changes in the engine.

refactor(web): delayed OSK initialization 🍕

refactor(web): osk inner-frame abstraction (help text vs std OSK) 🍕

Co-authored-by: Marc Durdin <marc@durdin.net>

feat(common/core): debug action index 🐞

Co-authored-by: Eberhard Beilharz <ermshiperete@users.noreply.github.com>

auto: increment master version to 15.0.88

refactor(linux): Refactor processing actions in separate methods 🚧

Adds some tests for Keyman Core for debugging, verifying contents of
the action list after every keystroke in the test.

Also refactors some of the test helper files to make it easier to
diagnose failing tests and share helper functions.

fix(ios): keyboard swapping