More renaming

Avoid usage of "Feature Flag" unless we are talking specifically about
the response from github features api. Otherwise, use terms like
"Toggleable features".

Note both "toggleable" and "togglable" appear to be valid spellings of
the word. I chose the first for no good reason.

src/testing-utils.ts

@@ -4,6 +4,7 @@ import * as sinon from "sinon";
 
 import * as apiClient from "./api-client";
 import * as CodeQL from "./codeql";
+import { Feature, FeatureEnablement } from "./feature-flags";
 import { Logger } from "./logging";
 import { HTTPError } from "./util";
 
@@ -168,3 +169,18 @@ export function mockCodeQLVersion(version) {
     },
   } as CodeQL.CodeQL;
 }
+
+/**
+ * Create a feature enablement instance with the specified set of enabled features.
+ *
+ * This should be only used within tests.
+ */
+export function createFeatureFlags(
+  enabledFeatures: Feature[]
+): FeatureEnablement {
+  return {
+    getValue: async (feature) => {
+      return enabledFeatures.includes(feature);
+    },
+  };
+}