Upgrade path/paint/contour data to storage buffers

Non-modern GL (including WebGL) is the only API that doesn't support storage buffers. Upgrade this data to storage buffers and let the copy-to-texture codepath be a GL-specific polyfill. This is simpler, more memory efficient, and faster on modern APIs like Metal. It will also will enable us to clean up and fully integrate atomic mode.

Simplify some of our multi-language paradigms in the shaders while adding general support for storage buffers.

Also take this opportunity to do some much needed cleanup on the PLSRenderContextImpl and BufferRing APIs, including specifying the buffer update range during map() instead of unmap() now that we know what it will be upfront. Specifying the range during map() allows us to map buffers directly instead of using a shadow buffer on GL and D3D11.

Diffs=

.rive_renderer

@@ -1 +1 @@
-4873326d7c84c4961122998eee89af9fe0b8235f
+af151553e8e9eb0ca1f7d62d7178cf9cdc023d71