test(3p/nix): Port language test suite to Googletest

This moves the language test suite into Googletest by constructing
parameterised tests out of the same language snippets used for the
previous lang.sh evaluation.

So far this includes support for about 3/4 of all tests, specifically:

* all parser success/failure tests
* all evaluator failure tests

The evaluator success tests will be implemented in a subsequent commit,
because the output comparison contains a whole bunch of additional
logic that I did not want to cram in here.

Change-Id: Icec9f368366cdbaa53b4c7e4472b8b6e8dd72eba
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1278
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: isomer <isomer@tvl.fyi>
Tested-by: BuildkiteCI

third_party/nix/src/tests/dummy-store.hh

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <filesystem>
+
 #include "libstore/store-api.hh"
 
 namespace nix::tests {