LibJS: Allow anonymous functions as default exports

This requires a special case with names as the default function is
supposed to have a unique name ("*default*" in our case) but when
checked should have name "default".

Userland/Libraries/LibJS/Tests/modules/anon-func-decl-default-export.mjs

@@ -0,0 +1,26 @@
+try {
+    f();
+} catch (e) {
+    if (!(e instanceof ReferenceError)) throw e;
+    if (!e.message.includes("bindingUsedInFunction")) throw e;
+}
+
+let bindingUsedInFunction = 0;
+
+const immediateResult = f();
+const immediateName = f.name + "";
+
+import f from "./anon-func-decl-default-export.mjs";
+export default function () {
+    return bindingUsedInFunction++;
+}
+
+const postImportResult = f();
+const postImportName = f.name + "";
+
+export const passed =
+    immediateResult === 0 &&
+    postImportResult === 1 &&
+    bindingUsedInFunction === 2 &&
+    immediateName === "default" &&
+    postImportName === "default";

Userland/Libraries/LibJS/Tests/modules/basic-modules.js

@@ -202,6 +202,10 @@ describe("in- and exports", () => {
     test("import lexical binding before import statement behaves as initialized but non mutable binding", () => {
         expectModulePassed("./accessing-lex-import-before-decl.mjs");
     });
+
+    test("exporting anonymous function", () => {
+        expectModulePassed("./anon-func-decl-default-export.mjs");
+    });
 });
 
 describe("loops", () => {