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, 1 insertions, 0 deletions

diff --git a/examples/shader-toy/main.cpp b/examples/shader-toy/main.cpp
index c4424b294..8e377b42f 100644
--- a/examples/shader-toy/main.cpp
+++ b/examples/shader-toy/main.cpp
@@ -315,6 +315,7 @@ Result initialize()
     gWindow->events.sizeChanged = Slang::Action<>(this, &ShaderToyApp::windowSizeChanged);
 
     IDevice::Desc deviceDesc;
+    deviceDesc.deviceType = DeviceType::Vulkan;
     Result res = gfxCreateDevice(&deviceDesc, gDevice.writeRef());
     if(SLANG_FAILED(res)) return res;