Pass --zig-lib-dir config option to the build runner

[GalaxyShard]

Without this patch, the build runner fails to run if build scripts depend on a modified zig library directory even if the config file specifies a different library directory, for example if the project depends on patches to the Zig build system.

I tested this change on a project of mine with a blank config file and with a config file that sets zig_lib_path; it seems to work correctly in both scenarios.

[Techatrix]

This is missing a check here:

zls/src/DocumentStore.zig

Lines 814 to 816 in 61c7147

	if (self.config.zig_exe_path == null) return;
	if (self.config.build_runner_path == null) return;
	if (self.config.global_cache_path == null) return;

and an assertion here:

zls/src/DocumentStore.zig

Lines 1039 to 1041 in 61c7147

	std.debug.assert(self.config.zig_exe_path != null);
	std.debug.assert(self.config.build_runner_path != null);
	std.debug.assert(self.config.global_cache_path != null);

[Techatrix]

👍