Delete the simple gradient texture transfer

The previous approach of transferring simple gradients directly to the texture, and then rendering complex gradients had various inefficiencies:

  * The texture resource had to be transitioned to and from TRANSFER_DST.

  * It required a pipeline barrier on the transfer stage.

  * The gradient texture had to be created with transfer capabilities.

  * Unnecessary code complexity.

It also ran into platform bugs on various Android and Unreal environments.

This PR just removes the texture transfer entirely and renders simple gradients at the same time we render complex ones. Rendering the simple ramps requires us to upload more data to the GPU, but the tradeoffs should be worth it.

Diffs=
792049458c Delete the simple gradient texture transfer (#8844)

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@@ -1 +1 @@
-a065ebe0464db4d8ed4dd28ff0d6b5e22b09405a
+792049458cf90c0fb3f06a34080db079281bd2e7