Libraries/LibCpp: Add parser test for out-of-line function definitions

Author: https://github.com/itamar8910
Commit: 610b380515
Pull-request: https://github.com/SerenityOS/serenity/pull/12730

Userland/Libraries/LibCpp/Tests/parser/out-of-line.cpp

@@ -0,0 +1,10 @@
+
+
+class A
+{
+    bool foo();
+};
+
+bool A::foo() {
+    return true;
+}