Fix unqualified unused import false positive

If we exposed a symbol in an import and used it both unqualified
and qualified, we'd produce an unused warning false positive.

This happened because we were using a single bit flag to determine
whether a value was used qualified or unqualified.

crates/compiler/load_internal/tests/test_load.rs

@@ -1079,6 +1079,38 @@ fn unused_imports() {
     )
 }
 
+#[test]
+fn used_exposed_and_qualified() {
+    let modules = vec![
+        (
+            "Dep.roc",
+            indoc!(
+                r#"
+            interface Dep exposes [one] imports []
+
+            one = 1
+            "#
+            ),
+        ),
+        (
+            "Main.roc",
+            indoc!(
+                r#"
+        interface Main exposes [qualified, exposed] imports []
+
+        import Dep exposing [one]
+
+        qualified = Dep.one
+        exposed = one
+            "#
+            ),
+        ),
+    ];
+
+    let result = multiple_modules("used_exposed_and_qualified", modules);
+    assert!(result.is_ok())
+}
+
 #[test]
 fn import_with_alias() {
     let modules = vec![