Rename GPU to raster thread in PerformanceOverlay (flutter/engine#17148)

Rename GPU to raster thread in PerformanceOverlay and update goldens.

engine/src/flutter/flow/layers/performance_overlay_layer.cc

@@ -89,7 +89,7 @@ void PerformanceOverlayLayer::Paint(PaintContext& context) const {
   VisualizeStopWatch(
       *context.leaf_nodes_canvas, context.raster_time, x, y, width,
       height - padding, options_ & kVisualizeRasterizerStatistics,
-      options_ & kDisplayRasterizerStatistics, "GPU", font_path_);
+      options_ & kDisplayRasterizerStatistics, "Raster", font_path_);
 
   VisualizeStopWatch(*context.leaf_nodes_canvas, context.ui_time, x, y + height,
                      width, height - padding,

engine/src/flutter/flow/layers/performance_overlay_layer_unittests.cc

@@ -163,7 +163,7 @@ TEST_F(PerformanceOverlayLayerTest, SimpleRasterizerStatistics) {
 
   layer->Paint(paint_context());
   auto overlay_text = PerformanceOverlayLayer::MakeStatisticsText(
-      paint_context().raster_time, "GPU", "");
+      paint_context().raster_time, "Raster", "");
   auto overlay_text_data = overlay_text->serialize(SkSerialProcs{});
   SkPaint text_paint;
   text_paint.setColor(SK_ColorGRAY);