Fixes #4558.

This makes a number of fixes to get the context help working correctly
in Keyman 14:

1. Adds support for `redirect:` header in help .md files so that we can
   do redirects for the context content in Keyman for Windows help in the
   lua filters.
2. Renames Keyman for Windows help files to .htm, because that's what
   the .chm format is expecting, and what Delphi assumes for its .chm
   integration, and thus splits the html and htm lua filters.
3. Renames and makes more consistent the various context help pages.
4. Adds redirects for all pages that have sufficient content on other
   pages.
5. Fixes the instantiation of help in various Keyman for Windows forms.
6. Defaults to opening help from the Keyman source repo if the calling
   app is running in the source repo (this is just a development-side
   tweak that simplifies my life).

chore(linux): Fix some lintian warnings for Debian package

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

fix(web): use language code correctly in toolbar

The previous setting didn't complain if uscan didn't find a signature
which doesn't help security wise. It would still allow an attacker
to modify the source package. This change now requires a valid
signature for the source package.

Fixes #4566.

When the toolbar shows a differentiation for the language code, it was
not using the correct minification-safe property name, which resulted in
`[undefined]` being displayed instead.

auto: increment beta version to 14.0.254

fix(developer): Expand filenames before load

chore(linux): Improve Sentry environment setting

chore(android/app): Update whatsnew with available display languages

fix(windows): incxstr could run over buffer with malformed data

* List available display languages
* Add KMEA breaking changes

Fixes #4583.

fix(ios): support for direct downloads of .kmp packages from within the in-app browser

fix(developer): tidy up expansions tests

fix(windows): PreservedKeyMap::MapUSCharToVK line order bug

fix(android): Localize Toast notifications

Fixes #4591.

I fixed incxstr in 4 places:

1. Common/Core: kmx_xstring.cpp
2. Engine: xstring.cpp
3. Test project importkeyboard importkeyboard.cpp
4. Test project m-to-p m-to-p.cpp

I updated mcompile to remove its own copy of incxstr (identical to that
in xstring.cpp) to reduce WETness but opted not to do so for the test
apps, which are pretty much throwaway anyway.

I note that there is more work we could do here; we need to check every
character as we increment so we don't miss a `U+0000` end of string with
malformed data. But I would like to tackle that as a separate job at
some point in the future after Core integration.

feat(developer): &CasedKeys system store

fix(android/app): Fix welcome.htm responsiveness

I discovered this while working on #4586. The code in question was
updating `*puKey` and then trying to dereference the array on the basis
of its new value, which (a) would give the wrong result, and (b) could
be reading off the end of the array (although not crashing it seems),
e.g. for `"` -> `VK_QUOTE`, which has a value of `0xDE`.

I am guessing that the reason we have not seen any bug reports on this
is that the keystroke handler falls back to an alternate code path, so
in the vast majority of cases, keyboards would continue to work
correctly. Furthermore, the test was just for truthiness of the `BOOL`
so probably at least 50% of the time we'd have been okay anyway. Or
something. Anyway, I reckon this is better.

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

auto: increment beta version to 14.0.253

When running from source we set the environment to `local` when
reporting to Sentry. This change also adds the package version and
the tier as additional Sentry tags.

This is a follow-up of PR #4581.

chore(linux): Don't report to Sentry in dev environment

fix(linux): Improve version number

fix(common/models): fixes application of suggestions immediately after a backspace

Cleaning up unused string failed_to_access_downloaded_file