Fixes#5700.
Adds support for arm64 (M1) to textinputsource in the Keyman app. All
other executables are already fat with support for both x86_64 and
arm64.
The installer did not work on downlevel versions
of macOS as the compile in Script Editor produced
a 10.15-compatible version. Now we build the app
directly from source with osacompile and bundle
that instead.
First steps towards a clean install script
for Keyman for Mac. Some steps still out-
of-order for now, particularly opening
System Preferences to allow Keyman before
Keyman has run for first time.
