test(schematics): key the compile host on the path TypeScript asks for

The four "output compiles" specs failed on Windows only. `path.resolve` returns
backslashes there, TypeScript rewrites a root name's separators before asking the
compiler host for that file, and the host's exact-match comparison then missed its
own in-memory file. Every Windows job reported TS6053 for a file it had been handed.

Reproduced on macOS by keying the host on a backslash path, since TypeScript's
slash rewriting is not limited to Windows.

Author: armando-navarro

src/schematics/update/v21/vertexai-to-ai.jasmine.ts

@@ -129,7 +129,7 @@ describe('rewriteVertexAIToAI', () => {
      * node_modules the way it would in a user's workspace.
      */
     const compile = (source: string): string[] => {
-      const filePath = resolve('migrated-output.ts');
+      const filePath = resolve('migrated-output.ts').replace(/\\/g, '/');
       const host = typescript.createCompilerHost(compilerOptions, true);
       const readFromDisk = host.getSourceFile.bind(host);
       const existsOnDisk = host.fileExists.bind(host);