Add test for `RayTCurrent`

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In `Test\Feature\HLSLLib` create, if applicable: (reference the HLSL headers for the types supported by the intrinsic)
- [ ] Test for 16 bit int types (`RayTCurrent.int16.test`)
- [ ] Test for Half type (`RayTCurrent.fp16.test`)
- [ ] Test for 32 bit types (`RayTCurrent.32.test`)
- [ ] Test for 64 bit int types (`RayTCurrent.int64.test`)
- [ ] Test for Double type (`RayTCurrent.fp64.test`)

A .test file should contain
- [ ] a source portion; if multiple .test files can use the same source, it can go in its own file and be referenced in the run portion of each .test file instead.
```
#--- source.hlsl

StructuredBuffer In : register(t0);
RWStructuredBuffer Out : register(u1);

[numthreads(1,1,1)]
void main() {
// A single test can test for all scalar/vector length as shown here.
Out[0] = length(In[0]); // Test float4
Out[1] = length(In[1].x); // Test float
Out[2] = length(In[1].yzw); // Test float3
Out[3] = length(In[1].yz); // Test float2
}
```
- [ ] a yaml portion; if multiple .test files can use the same YAML, it can go in its own file and be referenced in the run portion of each .test file instead.
```
//--- pipeline.yaml

---
Shaders:
- Stage: Compute
Entry: main
DispatchSize: [1, 1, 1]
Buffers:
- Name: In
Format: Float32
Stride: 16
Data: [ 4, 4, 4, 4, 3.14159, 0, 5, 12 ]
- Name: Out
Format: Float32
Stride: 4
ZeroInitSize: 12
- Name: ExpectedOut # The result we expect
Format: Float32
Stride: 4
Data: [ 8, 3.14159, 13, 5 ]
Results: # A test might have more than 1 result.
- Result: Test1
Rule: BufferFuzzy # there is also a BufferExact rule
ULPT: 1
Actual: Out
Expected: ExpectedOut
DescriptorSets:
- Resources:
- Name: In
Kind: StructuredBuffer
DirectXBinding:
Register: 0
Space: 0
VulkanBinding:
Binding: 0
- Name: Out
Kind: RWStructuredBuffer
DirectXBinding:
Register: 1
Space: 0
VulkanBinding:
Binding: 1
...
#--- end
```
- [ ] A run portion; this will be unique to each .test file.
```
# RUN: split-file %s %t
# RUN: %dxc_target -T cs_6_5 -Fo %t.o %t/source.hlsl
# RUN: %offloader %t/pipeline.yaml %t.o
```
Tests for 16 bit floating point should have a `# REQUIRES: Half`. Also add `-enable-16bit-types` to the RUN line.
Tests for 16 bit integer should have a `# REQUIRES: Int16`. Also add `-enable-16bit-types` to the RUN line.
Tests for 64 bit floating point should have a `# REQUIRES: Double`.
Tests for 64 bit integer should have a `# REQUIRES: Int64`.

Start in Test\Feature\HLSLLib and consult the HLSL headers to identify the types supported by RayTCurrent. Create the applicable .test files with source, YAML, and per-file RUN portions, adding the stated REQUIRES markers and flags for 16- and 64-bit types. Run the listed split-file, dxc_target, and offloader commands; done means each applicable type has a passing test.

Written by the indexing model from the issue text.