perf(ivy): avoid generating selectors array for directives without a selector (#33431)

Now that we've replaced `ngBaseDef` with an abstract directive definition, there are a lot more cases where we generate a directive definition without a selector. These changes make it so that we don't generate the `selectors` array if it's going to be empty.

PR Close #33431

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

@@ -516,8 +516,7 @@ runInEachFileSystem(os => {
 
       const jsContents = env.getContents('test.js');
       expect(jsContents)
-          .toContain(
-              'i0.ɵɵdefineDirective({ type: TestBase, selectors: [], inputs: { input: "input" } });');
+          .toContain('i0.ɵɵdefineDirective({ type: TestBase, inputs: { input: "input" } });');
 
       const dtsContents = env.getContents('test.d.ts');
       expect(dtsContents)