Fix gitignores for test fixture package configs (#3799)

* fix gitignore for test fixtures

* remove broken lines from top level gitignore

Author: jakemac53

.gitignore

@@ -7,10 +7,6 @@ pubspec.lock
 # Common build output
 /*/build/
 
-# Include package config files from tests which are hand coded
-!build_runner_core/test/fixtures/**/.dart_tool/package_config.json
-!build_runner_core/test/fixtures/**/pubspec.lock
-
 # Extra files from dart2js that we don't want
 build_runner/lib/src/server/graph_viz_main.dart.js.deps
 build_runner/lib/src/server/graph_viz_main.dart.js.tar.gz

build_runner_core/test/fixtures/.gitignore

@@ -0,0 +1,10 @@
+# Take special care to include the .dart_tool/package_config.json files and
+# only those.
+
+# Re-include the .dart_tool dir (can't unexclude files if their parent dir is
+# ignored).
+!/*/.dart_tool
+# Exclude everything under the .dart_tool (but not the dir itself!).
+/*/.dart_tool/*
+# Re-include the package config file.
+!/*/.dart_tool/package_config.json