Fixes#10615 (surrogate handling, km_core_state_context_set_if_needed).
Fixes#10616 (markers in app context, in unit tests)
Fixes#10617 (memory leak in replace_context).
The surrogate handling and markers in app context bugs were quite
tangled, so opted to fix those both together in one commit. The memory
leak was spotted while verifying the changes for surrogate handling.
Surrogates were not handled in is_context_unchanged, and opted to
refactor to work directly with km_core_context_item arrays rather than
continue with the string-based comparison, for simplicity.
While writing the corresponding unit tests, realised that the
app_context checks were incorrect in a number of existing tests, and so
fixed up the existing tests at the same time as writing up the new
tests. The only changes to core for this were to add assertions for the
app_context to ensure that markers are not inadvertently added.
Fixes#10582.
Returned struct from the `km_core_state_get_actions()` API is now owned
by the state object. This is a change in API contract. The corresponding
`km_core_actions_dispose()` API has been made private, because there is
never any need for API consumers to call it. As this change is happening
in alpha, we won't bump the ABI version.
`state->app_context` is now guaranteed to be in sync with
`state->context` after `km_core_process_event()`, with the actions
struct populated at that point.
The next and final step in this refactor is to remove the actions queue
altogether from the Core and make that a kmn-only concept, but that will
wait until 18.0. The only consumers of the actions queue are the
kmn-specific interactive debugger in Keyman Developer, and kmn-specific
Input Method eXtensions in Keyman Engine for Windows.
