Fix capture conversion in lenient mode.

...by always performing capture conversion in _strict_ mode, where there
is a better-defined hierarchy (non-null < unspecified < nullable, with
no "but also unspecified < non-null if you want).

Fixes jspecify#193

src/main/java/com/google/jspecify/nullness/NullSpecAnnotatedTypeFactory.java

@@ -531,6 +531,14 @@ public boolean isParametricQualifier(AnnotationMirror qualifier) {
     }
   }
 
+  @Override
+  public AnnotatedTypeMirror applyCaptureConversion(
+      AnnotatedTypeMirror type, TypeMirror typeMirror) {
+    return this == withLeastConvenientWorld
+        ? super.applyCaptureConversion(type, typeMirror)
+        : withLeastConvenientWorld.applyCaptureConversion(type, typeMirror);
+  }
+
   @Override
   protected TypeHierarchy createTypeHierarchy() {
     return new NullSpecTypeHierarchy(