Adapt Go tests to `codeql test`

These changes make the tests work with the coming `codeql test` support.

The `queries.xml` file defines which extractor the `codeql test`
runner will use to extract databases for the tests. In the future one
will be able to write this information in `qlpack.yml`, but we can't
do that immediately because the _existing_ CodeQL tooling would refuse
to parse a `qlpack.yml` that has the new field in it.

codeql-extractor.yml

@@ -14,3 +14,4 @@ file_types:
     display_name: Go
     extensions:
       - .go
+legacy_qltest_extraction: true

codeql-tools/index.cmd

@@ -0,0 +1,7 @@
+@echo off
+SETLOCAL EnableDelayedExpansion
+
+type NUL && "%CODEQL_EXTRACTOR_GO_ROOT%/tools/%CODEQL_PLATFORM%/go-extractor.exe" -mod=vendor ./...
+exit /b %ERRORLEVEL%
+
+ENDLOCAL

codeql-tools/index.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+set -eu
+
+if [ "$CODEQL_PLATFORM" != "linux64" ] && [ "$CODEQL_PLATFORM" != "osx64" ] ; then
+    echo "Automatic build detection for $CODEQL_PLATFORM is not implemented."
+    exit 1
+fi
+
+"$CODEQL_EXTRACTOR_GO_ROOT/tools/$CODEQL_PLATFORM/go-extractor" -mod=vendor ./...

ql/test/queries.xml

@@ -0,0 +1 @@
+<queries language="go"/>