Relates to #9999.

Establishes functions, unit test sources, normalization entry point and
an effectively no-op unit test for normalization support.

Relates to #9999.

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

Relates to #9999.

feat(core): normalize input context 🌱

refactor(mac): remove unused context calls 🌱

refactor(windows): use `km_core_state_context_debug` 🌱

refactor(linux): use `km_core_state_context_debug` 🌱

feat(core): add `km_core_state_context_debug` API 🌱

Relates to #9999

chore(core): Merge branch 'feat/core/10365-context-debug' into feat/core/9999-normalization-of-context

Note: shifted minor changes from action_api.cpp to new
state_context_api.cpp.

Co-authored-by: Steven R. Loomis <srl295@gmail.com>

Note: resolved merge conflict with action_api.cpp by shifting new code
into state_context_api.cpp.

chore(core): Ignore C++ symbols

auto: increment master version to 17.0.245

We have a C API, but (internal) C++ template instantiations are visible
and so get flagged by `dpkg-gensymbols`. This change ignores the one
use of C++ by marking it optional. This is listed as a usage scenario
in the dpkg-gensymbols man page.

Note this requires a change how we call dpkg-gensymbols: if the `-O`
parameter is specified, the file is not treated as being a template file
(see man deb-src-symbols) and so the tags are not interpreted.
Additionally the file gets overwritten with the non-tag version. So this
change removes the `-O` parameter, and changes the archiving of the
generated file.

docs(linux): Update sample settings

fix(web): use KMW OSK font for "**" special-text in key hints

First half of #9999.

Adds support for normalization (to NFD) of input app context into the
cached context. The keyboard processor will work with the NFD cached
context.

Adds unit tests for the normalization as part of the LDML keyboard
processor test suite.

TODO:
* Comparing modified cached context to app context to determine the
  transform required to send to the app
* Handling illegal unicode and unpaired surrogates on input context

Adds the application context member of state and a corresponding,
failing unit test, which starts the process of verifying the handling
of the application context.

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

feat(developer): warn on gesture support for downlevel

refactor(core): Move `km_core_state_context_*` tests to separate file

Relates to #10365.

Relates to #10365.
Fixes #10378.