Allow a package depending on zls to skip 'git describe'

[pfgithub]

This lets someone build zls as a dependency of another package with b.installArtifact(b.dependency("zls", .{ .target = target, .optimize = optimize, .@"commit-hash" = @as([]const u8, "HASH") }).artifact("zls")) without requiring git or erroring if the git output isn't as expected

[Techatrix]

I would rather have a build option to specify the entire version string (See #2183). It can be used to also specify the pre release version to check whether nightly versions are older or newer than each other.