Reimplement Vulkan shader objects. (#1764)

* Reimplement Vulkan shader objects.

This change reimplements Vulkan shader objects in the `gfx` layer so that it is no longer layered on top of the `DescriptorSet` abstraction. Since this is the last implementation that uses `DescriptorSet`, the change also removes all `DescriptorSet` related API from public `gfx` interface.

The Vulkan implementation now passes all test cases, but it still have two issues:
1. The PushConstant setting is not correct, this is because we don't seem to be able to get correct reflection data about the size of push constants for an entry-point.
2. The `shader-toy` example can't run on Vulkan, because it currently sets nullptr to `Texture` bindings, and this change doesn't properly handle setting resource to null in `ShaderObject`s yet. If we can use the `nullDescriptor` feature on vulkan, this implementation will be simple. However we still want to decide whether we want to use a Vulkan 1.2 feature for this.

* Fix up

1 files changed, 0 insertions, 2 deletions

diff --git a/tools/platform/gui.h b/tools/platform/gui.h
index 970f3a4e8..ef5310cd4 100644
--- a/tools/platform/gui.h
+++ b/tools/platform/gui.h
@@ -26,8 +26,6 @@ private:
     Slang::ComPtr<gfx::ICommandQueue> queue;
     Slang::ComPtr<gfx::IRenderPassLayout> renderPass;
     Slang::ComPtr<gfx::IPipelineState>       pipelineState;
-    Slang::ComPtr<gfx::IDescriptorSetLayout> descriptorSetLayout;
-    Slang::ComPtr<gfx::IPipelineLayout>      pipelineLayout;
     Slang::ComPtr<gfx::ISamplerState>        samplerState;
 };