eng: fix snapshot tests in macos webkit for real? (#193734)

Second attempt at this, which should work. Stop trying to use
exposeFunction, which seems to work poorly on macOS webkit in CI, and
just run a server with HTTP endpoints to do the "RPC."

Reuses Alex's "yaserver" module that we were already using for other
tests. Uses a secure random prefix for security in each run.

test/unit/browser/renderer.html

@@ -51,7 +51,7 @@
 		const baseUrl = window.location.href;
 		require.config({
 			catchError: true,
-			baseUrl: new URL('../../../src', baseUrl).href,
+			baseUrl: urlParams.get('baseUrl'),
 			paths: {
 				vs: new URL(`../../../${!!isBuild ? 'out-build' : 'out'}/vs`, baseUrl).href,
 				assert: new URL('../assert.js', baseUrl).href,
@@ -116,6 +116,27 @@
 			runner.on('pending', test => window.mocha_report('pending', serializeRunnable(test)));
 		};
 
+		const remoteMethods = [
+			'__readFileInTests',
+			'__writeFileInTests',
+			'__readDirInTests',
+			'__unlinkInTests',
+			'__mkdirPInTests',
+		];
+
+		for (const method of remoteMethods) {
+			const prefix = window.location.pathname.split('/')[1];
+			globalThis[method] = async (...args) => {
+				const res = await fetch(`/${prefix}/remoteMethod/${method}`, {
+					body: JSON.stringify(args),
+					method: 'POST',
+					headers: { 'Content-Type': 'application/json' }
+				});
+
+				return res.json();
+			}
+		}
+
 
 		async function loadModules(modules) {
 			for (const file of modules) {
@@ -129,25 +150,8 @@
 			}
 		}
 
-		/**
-		 * There is some bug in WebKit on macOS in CI only that causes the first
-		 * invokation of the file functions to (sometimes) take an inordinately
-		 * long period of time to run. Get around this by invoking them here.
-		 */
-		async function doIoWarmup() {
-			const dir = url.searchParams.get('ioWarmup');
-			if (!dir) {
-				return;
-			}
-
-			// these are the only two functions actually used in CI presently:
-			await __readFileInTests(dir + '/' + 'renderer.html');
-			await __readDirInTests(dir);
-		}
-
 		window.loadAndRun = async function loadAndRun({ modules, grep }, manual = false) {
 			// load
-			await doIoWarmup();
 			await loadModules(modules);
 			// await new Promise((resolve, reject) => {
 			// 	require(modules, resolve, err => {