Debian defines multiple similar environment variables. Libraries
are expected in `/usr/lib/i386-linux-gnu`. `DEB_TARGET_MULTIARCH`
gives that value, whereas the previous `DEB_TARGET_GNU_TYPE` gives
`i686-linux-gnu` which then results in our libraries not being found.
This change makes the necessary adjustments so that the package build
works with the new `build.sh` script. We no longer can rely on the
automatisms of debhelper. This change also adds a install target
to `build.sh`, and copies some files from the Keyman root directory
to the desktop directory because when package building we only
have access to the files in common/core/desktop. Along the same lines
it removes embedding `build-utils.h` from `build.sh`. Instead we set
the version and tier locally.
The packages in the official Debian repos have slightly more
up-to-date metadata. This change adjusts our metadata.
This includes the change from Debian repo to let debhelper (>= 10.3)
handle the meson build of keyman-keyboardprocessor.
