`countbits` intrinsic does not support vector arguments

[chaoticbob]

Slang currently does not support the variant of countbits that takes vector arguments:

shader.hlsl(15): error 30019: expected an expression of type 'uint', got 'vector<uint,2>'
    uint2 cb2 = countbits(var2);
                          ^~~~
shader.hlsl(16): error 30019: expected an expression of type 'uint', got 'vector<uint,3>'
    uint3 cb3 = countbits(var3);
                          ^~~~
shader.hlsl(17): error 30019: expected an expression of type 'uint', got 'vector<uint,4>'
    uint4 cb4 = countbits(var4);

Frequently used intrinsic, the vector argument variants should be supported.

Shader

cbuffer InputVars {
    uint1  var1;
    uint2  var2;
    uint3  var3;
    uint4  var4;
};

float4 main() : SV_TARGET{
    uint1 cb1 = countbits(var1);
    uint2 cb2 = countbits(var2);
    uint3 cb3 = countbits(var3);
      uint4 cb4 = countbits(var4);
    return float4((float)cb1.x, (float)cb2.x, (float)cb3.x, (float)cb4.x);
}

Reference: https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/countbits