[llvm] [DirectX] Update "dx.TypedBuffer" docs to include a "signed" bit (PR #100695)

[Damyan Pepper via llvm-commits]

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@@ -106,9 +106,10 @@ used for DXIL's RawBuffers and StructuredBuffers. We call the latter
 "RawBuffer" to match the naming of the operations, but it can represent both
 the Raw and Structured variants.
 
-For TypedBuffer, the element type must be an integer or floating point type.
-For RawBuffer the type can be an integer, floating point, or struct type.
-HLSL's ByteAddressBuffer is represented by an `i8` element type.
+For TypedBuffer, the element type must be an scalar integer or floating point
+type, or a vector of at most 4 such types. For RawBuffer the type can be an
+integer, floating point, vecvtor, or struct type. HLSL's ByteAddressBuffer is
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damyanp wrote:

```suggestion
integer, floating point, vector, or struct type. HLSL's ByteAddressBuffer is
```

https://github.com/llvm/llvm-project/pull/100695