Update Slang-RHI/slang (shader-slang#5701)

* Update Slang-RHI/slang

This brings in new fixes for WebGPU.
In particular, the "use_dxc" toggle is now used, which should enable these tests to run on
WebGPU, if f16 is otherwise supported:

- `tests/language-feature/generics/variadic-0.slang`
- `tests/language-feature/generics/tuple.slang`

This closes shader-slang#5605.

* Disable tests/autodiff/float-cast.slang for wgpu

This test was previously not running for WebGPU because it required the 'half' render
feature, and Slang-RHI was previously not reporting it.

With the Slang-RHI update, the test now runs on WebGPU.
It now fails because the test is using 'double' which is just not supported on WebGPU.

Thus this commit disables the test.

Author: aleino-nv

external/slang-rhi

@@ -1,5 +1,7 @@
 //TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type -render-features half
 //TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type -render-features half
+// Not supported in WGSL: Double and other unsupported scalar types
+//DISABLE_TEST(compute):COMPARE_COMPUTE_EX:-wgpu
 
 //TEST_INPUT:ubuffer(data=[0 0 0 0 0], stride=4):out,name=outputBuffer
 RWStructuredBuffer<float> outputBuffer;