Removed clamping from dithering (#56140)

tests: flutter/flutter#157643
fixes revert from flutter/flutter#153976

The pixel format will clamp if it needs to anyway so this isn't
necessary.

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Author: gaaclarke

impeller/compiler/shader_lib/impeller/dithering.glsl

@@ -45,9 +45,6 @@ vec4 IPOrderedDither8x8(vec4 color, vec2 dest) {
   // Apply the dither to the color.
   color.rgb += dither * kDitherRate;
 
-  // Clamp the color values to [0,1].
-  color.rgb = clamp(color.rgb, 0.0, 1.0);
-
   return color;
 }
 

impeller/tools/malioc.json

@@ -586,7 +586,7 @@
             "shortest_path_cycles": [
               0.5,
               0.109375,
-              0.296875,
+              0.28125,
               0.5,
               0.0,
               0.25,
@@ -596,9 +596,9 @@
               "load_store"
             ],
             "total_cycles": [
-              1.4249999523162842,
+              1.40625,
               0.862500011920929,
-              1.4249999523162842,
+              1.40625,
               0.875,
               4.0,
               0.25,
@@ -636,7 +636,7 @@
             "longest_path_cycles": [
               0.5,
               0.109375,
-              0.125,
+              0.109375,
               0.5,
               0.0,
               0.25,
@@ -658,7 +658,7 @@
             "shortest_path_cycles": [
               0.5,
               0.109375,
-              0.125,
+              0.109375,
               0.5,
               0.0,
               0.25,
@@ -671,7 +671,7 @@
             "total_cycles": [
               0.5,
               0.109375,
-              0.125,
+              0.109375,
               0.5,
               0.0,
               0.25,
@@ -6298,7 +6298,7 @@
             "shortest_path_cycles": [
               0.5625,
               0.203125,
-              0.265625,
+              0.25,
               0.5625,
               0.0,
               0.25,
@@ -6308,9 +6308,9 @@
               "load_store"
             ],
             "total_cycles": [
-              0.71875,
+              0.699999988079071,
               0.40625,
-              0.71875,
+              0.699999988079071,
               0.5625,
               4.0,
               0.25,
@@ -6768,7 +6768,7 @@
             "shortest_path_cycles": [
               0.5625,
               0.21875,
-              0.28125,
+              0.265625,
               0.5625,
               0.0,
               0.25,
@@ -6778,9 +6778,9 @@
               "load_store"
             ],
             "total_cycles": [
-              0.71875,
+              0.699999988079071,
               0.421875,
-              0.71875,
+              0.699999988079071,
               0.625,
               4.0,
               0.25,