Problem description
It appears that we are adding the same OpCapability more than once unnecessarily.
As an example, when we call a texture sampling function, we add the required capability by calling a function, "__requireComputeDerivative()".

    T Sample(vector<float, Shape.dimensions+isArray> location)
    {
        __requireComputeDerivative();
        __target_switch
    ... omit the rest ...

When we call the function more than once, the emitted SPIR-V code gets more than one of the same lines.
I am putting the example below,

; SPIR-V
; Version: 1.5
; Generator: Khronos; 40
; Bound: 2805
; Schema: 0
OpCapability Sampled1D
OpCapability ImageQuery
OpCapability ImageBuffer
OpCapability StorageImageReadWithoutFormat
OpCapability StorageImageWriteWithoutFormat
OpCapability StorageImageMultisample
OpCapability ComputeDerivativeGroupQuadsNV
OpCapability ComputeDerivativeGroupQuadsNV
OpCapability ComputeDerivativeGroupQuadsNV
OpCapability ComputeDerivativeGroupQuadsNV
OpCapability ComputeDerivativeGroupQuadsNV
...omit the rest ...

Note that the same line is added multiple times near the end.

Ideally we should avoid adding the same line more than once.

Repro step
This can be reproduced with one of existing tests that calls Sample or any equivalent.
The examples are following,

1. tests/glsl-intrinsic/intrinsic-texture.slang
2. tests/glsl-intrinsic/compute-derivative/intrinsic-derivative-function-in-compute.slang

Goal
We should avoid adding the same OpCapability more than once.