This introduces the concept of a "dist resource" (specifically a
`GhosttyDist.Resource` type). This is a resource that may be present in
dist tarballs but not in the source tree. If the resource is present and
we're not in a Git checkout, then we use it directly instead of
generating it.
This is used for the first time in this commit for the gresource c/h
files, which depend on a variety of external tools (blueprint-compiler,
glib-compile-resources, etc.) that we do not want to require downstream
users/packagers to have and we also do not want to worry about them
having the right versions.
This also adds a check for `distcheck` to ensure our distribution
contains all the expected files.
This moves the source tarball creation process into the Zig build system
and follows the autotools-standard naming conventions of `dist` and
`distcheck`.
The `dist` target creates a source tarball in the `PREFIX/dist`
directory. The tarball is named `ghostty-VERSION.tar.gz` as expected by
standard source tarball conventions.
The `distcheck` target does the same as `dist`, but also takes the
resulting tarball, extracts it, and runs tests on the extracted source
to verify the source tarball works as expected.
This commit also updates CI:
1. Tagged releases now use the new `zig build distcheck` command.
2. Tip releases now use the new `zig build dist` command.
3. A new test build tests that source tarball generation works on
every commit.
