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#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.
Relates to #9999.
Fixes#10384.
The context API endpoints should no longer be considered as part of the
standard Core API. The only consumers that have a need to access these
APIs are the IMX integration in Engine for Windows, and the Keyman
Developer Debugger.
These symbols are currently used by Developer:
* `km_core_context` struct
* `km_core_context_type` enum
* `km_core_context_item` struct
* `KM_CORE_CONTEXT_ITEM_END` macro
* `km_core_state_context()`
* `km_core_context_set()`
* `km_core_context_clear()`
These symbols are currently used by Windows IMX:
* `km_core_context` struct
* `km_core_context_type` enum
* `km_core_context_item` struct
* `KM_CORE_CONTEXT_ITEM_END` macro
* `km_core_context_items_dispose()`
* `km_core_context_item_list_size()`
* `km_core_state_get_intermediate_context()`
The following functions and symbols are moving to
keyman_core_api_context.h:
* `km_core_context` struct
* `km_core_context_type` enum
* `km_core_context_item` struct
* `KM_CORE_CONTEXT_ITEM_END` macro
* `km_core_state_context()` function
* `km_core_state_get_intermediate_context()` function
* `km_core_context_set()` function
* `km_core_context_clear()` function
* `km_core_context_get()` function
* `km_core_context_items_from_utf16()` function
* `km_core_context_items_from_utf8()` function
* `km_core_context_items_to_utf8()` function
* `km_core_context_items_to_utf16()` function
* `km_core_context_items_to_utf32()` function
* `km_core_context_items_dispose()` function
* `km_core_context_length()` function
* `km_core_context_append()` function
* `km_core_context_shrink()` function
* `km_core_context_item_list_size()` function
