fix(compiler-cli): enable @types discovery in incremental rebuilds (#39011)

Prior to this fix, incremental rebuilds could fail to type check due to
missing ambient types from auto-discovered declaration files in @types
directories, or type roots in general. This was caused by the
intermediary `ts.Program` that is created for template type checking,
for which a `ts.CompilerHost` was used which did not implement the
optional `directoryExists` methods. As a result, auto-discovery of types
would not be working correctly, and this would retain into the
`ts.Program` that would be created for an incremental rebuild.

This commit fixes the issue by forcing the custom `ts.CompilerHost` used
for type checking to properly delegate into the original
`ts.CompilerHost`, even for optional methods. This is accomplished using
a base class `DelegatingCompilerHost` which is typed in such a way that
newly introduced `ts.CompilerHost` methods must be accounted for.

Fixes #38979

PR Close #39011

packages/compiler-cli/test/ngtsc/incremental_spec.ts

@@ -442,6 +442,27 @@ runInEachFileSystem(() => {
       // https://github.com/angular/angular/issues/30079), this would have crashed.
     });
 
+    // https://github.com/angular/angular/issues/38979
+    it('should retain ambient types provided by auto-discovered @types', () => {
+      // This test verifies that ambient types declared in node_modules/@types are still available
+      // in incremental compilations. In the below code, the usage of `require` should be valid
+      // in the original program and the incremental program.
+      env.tsconfig({fullTemplateTypeCheck: true});
+      env.write('node_modules/@types/node/index.d.ts', 'declare var require: any;');
+      env.write('main.ts', `
+        import {Component} from '@angular/core';
+
+        require('path');
+
+        @Component({template: ''})
+        export class MyComponent {}
+      `);
+      env.driveMain();
+      env.invalidateCachedFile('main.ts');
+      const diags = env.driveDiagnostics();
+      expect(diags.length).toBe(0);
+    });
+
     // https://github.com/angular/angular/pull/26036
     it('should handle redirected source files', () => {
       env.tsconfig({fullTemplateTypeCheck: true});