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-object/main.cpp b/examples/shader-object/main.cpp
index aaafc010a..4945de27b 100644
--- a/examples/shader-object/main.cpp
+++ b/examples/shader-object/main.cpp
@@ -136,6 +136,7 @@ int main()
     // interacting with the graphics API.
     Slang::ComPtr<gfx::IDevice> device;
     IDevice::Desc deviceDesc = {};
+    deviceDesc.deviceType = DeviceType::Vulkan;
     SLANG_RETURN_ON_FAIL(gfxCreateDevice(&deviceDesc, device.writeRef()));
 
     // Now we can load the shader code.