Do not consider UMD alias symbols as visible within external modules (#18049)

* Do not consider UMD alias symbols as visible within external modules in the symbol writer

* Minimal repro

tests/cases/compiler/importShouldNotBeElidedInDeclarationEmit.ts

@@ -0,0 +1,12 @@
+// @declaration: true
+// @filename: node_modules/umd.d.ts
+export as namespace UMD;
+
+export type Thing = {
+    a: number;
+}
+
+export declare function makeThing(): Thing;
+// @filename: index.ts
+import { makeThing } from "umd";
+export const thing = makeThing();