Extract functions for service worker usage, and add initial MSC3916 playwright test (when supported) (#12414)

* Send user credentials to service worker for MSC3916 authentication

* appease linter

* Add initial test

The test fails, seemingly because the service worker isn't being installed or because the network mock can't reach that far.

* Remove unsafe access token code

* Split out base IDB operations to avoid importing `document` in serviceworkers

* Use safe crypto access for service workers

* Fix tests/unsafe access

* Remove backwards compatibility layer & appease linter

* Add docs

* Fix tests

* Appease the linter

* Iterate tests

* Factor out pickle key handling for service workers

* Enable everything we can about service workers

* Appease the linter

* Add docs

* Rename win32 image to linux in hopes of it just working

* Use actual image

* Apply suggestions from code review

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Improve documentation

* Document `??` not working

* Try to appease the tests

* Add some notes

---------

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

test/utils/StorageAccess-test.ts

@@ -0,0 +1,55 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+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 "core-js/stable/structured-clone"; // for idb access
+import "fake-indexeddb/auto";
+
+import { idbDelete, idbLoad, idbSave } from "../../src/utils/StorageAccess";
+
+const NONEXISTENT_TABLE = "this_is_not_a_table_we_use_ever_and_so_we_can_use_it_in_tests";
+const KNOWN_TABLES = ["account", "pickleKey"];
+
+describe("StorageAccess", () => {
+    it.each(KNOWN_TABLES)("should save, load, and delete from known table '%s'", async (tableName: string) => {
+        const key = ["a", "b"];
+        const data = { hello: "world" };
+
+        // Should start undefined
+        let loaded = await idbLoad(tableName, key);
+        expect(loaded).toBeUndefined();
+
+        // ... then define a value
+        await idbSave(tableName, key, data);
+
+        // ... then check that value
+        loaded = await idbLoad(tableName, key);
+        expect(loaded).toEqual(data);
+
+        // ... then set it back to undefined
+        await idbDelete(tableName, key);
+
+        // ... which we then check again
+        loaded = await idbLoad(tableName, key);
+        expect(loaded).toBeUndefined();
+    });
+
+    it("should fail to save, load, and delete from a non-existent table", async () => {
+        // Regardless of validity on the key/data, or write order, these should all fail.
+        await expect(() => idbSave(NONEXISTENT_TABLE, "whatever", "value")).rejects.toThrow();
+        await expect(() => idbLoad(NONEXISTENT_TABLE, "whatever")).rejects.toThrow();
+        await expect(() => idbDelete(NONEXISTENT_TABLE, "whatever")).rejects.toThrow();
+    });
+});