Spawn a code-server instance for each test suite

This uses the current dev build by default but can be overidden with
CODE_SERVER_TEST_ENTRY (for example to test a release or some other
version).

Each instance has a separate state directory. This should make
parallelization work.

This also means you are no longer required to specify the password and
address yourself (or the extension directory once we add a test
extension). `yarn test:e2e` should just work as-is.

Lastly, it means the tests are no longer subject to yarn watch randomly
restarting.

test/e2e/browser.test.ts

@@ -1,7 +1,7 @@
-import { test, expect } from "./baseFixture"
+import { describe, test, expect } from "./baseFixture"
 
 // This is a "gut-check" test to make sure playwright is working as expected
-test.describe("browser", () => {
+describe("browser", () => {
   test("browser should display correct userAgent", async ({ codeServerPage, browserName }) => {
     const displayNames = {
       chromium: "Chrome",