[analyzer] Make ContextResolutionTest hermetic.

This change causes all tests derived from `ContextResolutionTest` to
register lint rules during `setUp` and de-register them during
`tearDown`, making these tests properly hermetic.

Previously, the first time a `ContextResolutionTest`-derived test was
run, its `setUp` would register lint rules, and then further
`ContextResolutionTest`-derived tests would not register them, meaning
that if any test was run in the interim that attempted to properly
clean up its lint registrations, it could provoke a later test
failure.

The new approach makes the tests more predictable and
comprehensible. There is a small performance penalty (running
`pkg/analyzer/test/test_all.dart` takes ~2.5% longer on my machine). I
the predictability and comprehensibility that we gain by making the
tests hermetic is worth this small performance cost.

Change-Id: I6a6a6964541ce43a5c5afd6d047bf250050f95c5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/464060
Auto-Submit: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: stereotype441

pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart

@@ -14,6 +14,7 @@ import 'package:analyzer/src/dart/analysis/driver_based_analysis_context.dart';
 import 'package:analyzer/src/dart/analysis/results.dart';
 import 'package:analyzer/src/dart/analysis/unlinked_unit_store.dart';
 import 'package:analyzer/src/dart/element/element.dart';
+import 'package:analyzer/src/lint/registry.dart';
 import 'package:analyzer/src/test_utilities/mock_sdk.dart';
 import 'package:analyzer/src/util/file_paths.dart' as file_paths;
 import 'package:analyzer/src/workspace/basic.dart';
@@ -73,8 +74,6 @@ class BlazeWorkspaceResolutionTest extends ContextResolutionTest {
 /// [AnalysisContextCollection] based implementation of [ResolutionTest].
 abstract class ContextResolutionTest
     with ResourceProviderMixin, ResolutionTest {
-  static bool _lintRulesAreRegistered = false;
-
   /// The byte store that is reused between tests. This allows reusing all
   /// unlinked and linked summaries for SDK, so that tests run much faster.
   /// However nothing is preserved between Dart VM runs, so changes to the
@@ -246,14 +245,14 @@ abstract class ContextResolutionTest
 
   @mustCallSuper
   void setUp() {
-    if (!_lintRulesAreRegistered) {
-      registerLintRules();
-      _lintRulesAreRegistered = true;
-    }
+    registerLintRules();
   }
 
   @mustCallSuper
   Future<void> tearDown() async {
+    for (var rule in Registry.ruleRegistry.rules) {
+      Registry.ruleRegistry.unregisterLintRule(rule);
+    }
     await disposeAnalysisContextCollection();
   }