test: add runtime field duplicate noop control

include/mbgl/style/sources/raster_array_source.hpp

@@ -52,6 +52,9 @@ public:
     // Validation convenience: advance using the next Source-owned preloaded
     // candidate. Android supplies no T0/T1 state and no GPU resource here.
     RasterArrayRuntimeFieldUpdateResult advanceRuntimeFieldWindow();
+    // Validation convenience: resubmit the current T1 through the formal
+    // update API. This must return Noop without changing the Source window.
+    RasterArrayRuntimeFieldUpdateResult repeatRuntimeFieldWindow();
     bool supportsLayerType(const LayerTypeInfo*) const override;
     mapbox::base::WeakPtr<Source> makeWeakPtr() override { return weakFactory.makeWeakPtr(); }