observability: add base for instrumentation + tests

This change adds the scaffolding for instrumentation
along with tests for the tracing mechanisms that'll
be used to trace the entire package.

Built from googleapis#2087
Updates googleapis#2079

observability-test/helper.ts

@@ -0,0 +1,34 @@
+/*!
+ * Copyright 2024 Google LLC. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {ContextManager, context} from '@opentelemetry/api';
+
+/**
+ * This utility exists as a test helper because mocha has builtin "context"
+ * and referring to context causes type/value collision errors.
+ */
+export function setGlobalContextManager(manager: ContextManager) {
+  context.setGlobalContextManager(manager);
+}
+
+/**
+ * This utility exists as a test helper because mocha has builtin "context"
+ * and referring to context causes type/value collision errors.
+ */
+export function disableContextAndManager(manager: ContextManager) {
+  manager.disable();
+  context.disable();
+}