With this change it's possible to build Keyman from the source tarball
by running `./build.sh` from the Keyman root directory.
When building Keyman as part of the Ubuntu/Debian packaging, we don't use
the toplevel `build.sh` file but instead call the build scripts in the
subdirectories. This omits building some components that are currently
not needed for running Keyman for Linux. The `dist.sh` script only
includes the necessary files in this case, distinguished by the `origdist`
parameter. This results in a significantly smaller tarball (2.5MB vs 51MB).
This change also enhances the `generate_tar_ignore_list` function so that
it is now possible to add `build` to the exclude list to ignore all
`build` subdirectories.
Fixes: #15544
Build-bot: skip
Test-bot: skip
This generates the `--tar-ignore`s to avoid having to manually maintain
the list when adding new files or folders for other platforms. Instead
now we have a list of files and directories to include, and a list of
exceptions to exclude from the includes. From that we generate the
tar-ignore list.
Fixes: #14563
Test-bot: skip
