Describe the pull request

This PR addresses several minor issues related to descriptor sets:

• The root parameter index is no longer stored on the descriptor set or push constants range layout. Instead the pipeline stores a root parameter index for each space. This makes it easier to re-use descriptor sets over multiple pipelines, as long as they remain compatible (which the application has to ensure).
• Push constants can now be used with compute shaders.
• In Vulkan, the reference to the parent pipeline layout for push constant ranges has been removed.