Add ui test for rust-lang#98938

Author: obeis

src/test/ui/traits/issue-98938.rs

@@ -0,0 +1,10 @@
+trait Foo {
+    fn bar() {}
+}
+
+fn main() {
+    Foo::bar();
+    //~^ ERROR type annotations needed
+
+    <_ as Foo>::bar();
+}

src/test/ui/traits/issue-98938.stderr

@@ -0,0 +1,9 @@
+error[E0283]: type annotations needed
+  --> $DIR/issue-98938.rs:6:5
+   |
+LL |     Foo::bar();
+   |     ^^^^^^^^ cannot call trait method as a free function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0283`.