check constexpr of the nested calls

[gtong-nv]

This change aims to report error when the nested func requires constexpr, and the caller calls wrapper func with non-cost params.
For example, the following should failed to compile because RWTexture2D::Load requires offset to be constexpr.

Texture2D<float3> input;
RWTexture2D<float3> output;

float3 LoadSourceColor(int2 offset) {
    int3 pixelPos = int3(0,0,0);
    return input.Load(pixelPos, offset);
}

[shader("compute")]
void Test() {
    float3 result = 0;

    [ForceUnroll]
    for (int i = 0; i < 3; i++) {
        //result += input.Load( int3(0,0,0), int2( i, i ));
        result += LoadSourceColor(int2( i, i ));
    }

    output[0] = result;
}

Fixes: #6370

[gtong-nv]

/format

[slangbot]

🌈 Formatted, please merge the changes from this PR

[juliusikkala]

I think this should be changedInThisInst |= checkInstConstExprRecursively(context, ii);, otherwise changedInThisInst may reset back to false if a later instruction didn't change.

[juliusikkala]

The recursion going through this line causes a stack overflow if a recursive function is given in input, like in tests/diagnostics/recursion.slang.

[kaizhangNV]

I'm wondering for all of those changedInThisInst = true; can we just early return? It doesn't look like we need to go through everything.