Fix adjustment of context buffer when buffer is full. This also accounts for deadkey or surrogate pairs.

* Also added 3 meson unit tests

Using numbers so debugging context will be clearer

Reproduces issue #2575 with a keyboardprcoessor unit test.

* Also fix build warning in `kmx_options.cpp` where  unsigned int `idx` is always `>= 0`

feat(linux): Keyboard options configuration dialog

fix(linux): Fix 'About' keyboard when missing copyright

Merge pull request #2580 from keymanapp/fix/windows/engine/2450-touch-keyboard-cancels-each-keystroke-beta

fix(windows): Windows touch keyboard would cancel on each keystroke

About keyboard fails to show when package copyright information is missing

Fixes #2450. When Keyman serialized input, it would cause the touch keyboard to cancel
because the touch keyboard thought the received event meant the user was touching the
physical keyboard. This resolves that problem, using a watch timer to check the visibility
of the touch input panel.

fix(linux) Remove cosmic and disco releases

19.04 Disco is EOL Jan 23, 2020 so also remove it

18.10 was end-of-life July 18, 2019 and launchpad is rejecting any further package updates for that version.

fix(web): default BKSP output targeting

fix(ios):  Fixes margins on keyboard in iOS 9/10

fix(web): Suggestion reordering for RTL languages

fix(common): RTL model specification

feat(ios):  Deeplink into Keyman settings for system keyboard setup

fix(ios): Now (eventually) uses sys pref for kbd clicks