Remove compiler support for `clearcontext`, `fix`, `switch` statements
and remove corresponding `CODE_` definitions, as well as `CODE_KEY`,
which was never used.
These four statements have never been documented and have either never
been implemented, or long been unsupported. An earlier change (#16445)
marked `clearcontext` and `fix` as deprecated for v19 onwards, but
deprecation for an undocumented language feature is an unnecessary step,
so have opted to remove altogether in v19 to reduce complexity. This
means that `VERSION_190` is used now only for compile target
deprecations.
Follows: #16445
Test-bot: skip
A string with leading delimiters passed into `u16tok()` would not skip
those delimiters. This impacted `&targets` store and other locations.
Note that this tightens input parameter checks for delimiters and
context as well.
Fixes: #13721
Test-bot: skip
* Move the following files from common/windows/cpp/include/ to
common/include/:
* keymanversion.h
* vkeys.h
* Move the following file from common/windows/cpp/ to common/cpp/:
* vkeys.cpp
* Move crc32.cpp,crc32.h into kmcmplib, as they are only used there.
* Remove unused ConvertUTF.c and ConvertUTF.h.
* Update references to the above files.
* Remove precompiled header refs from vkeys.cpp and change data type to
`char*` for types in vkeys.cpp (unless `USE_CHAR16_T` is defined), so
that it is more cross-platform accessible, update usages accordingly,
fixup project definitions accordingly.
* Remove unused define `KMN_KBP_EXPORTING` from kmcmplib/meson.build.
Fixes: #15565
Test-bot: skip
