Modify dimming threshold from 0.2 to 0.9.

We found that the original dimming threshold was relatively
small. When the dimming threshold exceeded 0.2, there were jitter
issues when exiting HDR videos or Ultra HDR photos to the recent
task. For better optimization, we raised the dimming threshold
from 0.2 to 0.9.

Bug: 321864707
Test: Manual

Change-Id: I3dfb987b149b05d4a3c15e14779c9caab4783d75
Signed-off-by: linkai <linkai@xiaomi.com>

Author: linkai

libs/renderengine/skia/SkiaRenderEngine.cpp

@@ -1022,7 +1022,7 @@ void SkiaRenderEngine::drawLayersInternal(
                                                   .fakeOutputDataspace = fakeDataspace}));
 
             // Turn on dithering when dimming beyond this (arbitrary) threshold...
-            static constexpr float kDimmingThreshold = 0.2f;
+            static constexpr float kDimmingThreshold = 0.9f;
             // ...or we're rendering an HDR layer down to an 8-bit target
             // Most HDR standards require at least 10-bits of color depth for source content, so we
             // can just extract the transfer function rather than dig into precise gralloc layout.