refactor(ivy): migrate ɵɵ prefix back to Δ (#30362)

Now that issues are resolved with Closure compiler, we can move back to our desired prefix of `Δ`.

PR Close #30362

packages/compiler-cli/test/compliance/mock_compiler_spec.ts

@@ -140,7 +140,7 @@ describe('mock_compiler', () => {
     expectEmit(
         result.source, `
     // TODO: this comment should not be taken into account
-    $r3$.ɵɵtext(0, "Hello!");
+    $r3$.Δtext(0, "Hello!");
     // TODO: this comment should not be taken into account
     `,
         'todo comments should be ignored');