Replaces kmcomp's package installer build infrastructure. While this is
mostly legacy, package installers are still used in adhoc distribution
scenarios, so we need to continue to support with the new kmc.

The package installer is a Windows self-extracting zip archive. The user
is expected to find setup-redist.exe and keymandesktop.msi themselves,
from the Keyman Developer release files. They are not included with
Keyman Developer, but are available as standalone downloads from
https://downloads.keyman.com/windows/.

`kmc build` has been updated to include two subcommands:
* `kmc build ldml-test-data`
* `kmc build windows-package-installer`

Both of these subcommands are a little long, but the use cases for them
are fairly narrow, so I believe this is okay. `kmc build-test-data` has
been removed, as `kmc build ldml-test-data` replaces it.