[Matrix] [HLSL] add a ICK_HLSL_Matrix_Truncation to handle matrix truncations in HLSL

[farzonl]

These are the truncation tests we should support:
https://godbolt.org/z/73vj6jMs7

essentially if the src is bigger than the dest even if destination is a scalar we should truncate. this should be handled via a new ICK_HLSL_Matrix_Truncation. tha should behave similarly to ICK_HLSL_Vector_Truncation since they share the same spec.

export int3x3 trunc_cast(int4x4 i44) {
    int3x3 i33 = (int3x3)i44;
    return i33;
}

export int3x2 trunc_cast2(int4x4 i44) {
    int3x2 i32 = (int3x2)i44;
    return i32;
}

export int2x3 trunc_cast3(int4x4 i44) {
    int2x3 i23 = (int2x3)i44;
    return i23;
}

export int2x2 trunc_cast4(int4x4 i44) {
    int2x2 i22 = (int2x2)i44;
    return i22;
}

export int2x1 trunc_cast5(int4x4 i44) {
    int2x1 i21 = (int2x1)i44;
    return i21;
}

export int trunc_cast6(int4x4 i44) {
    int i21 = (int)i44;
    return i21;
}

Originally posted by @farzonl in #162711

• Add standard conversion
• CK_HLSL_Matrix_Truncation needs APValue support
• Create the code gen truncation (Clang Matrix Type to Llvm vector)
• Create and apply the enums in all the right places.
• Write the required tests using the ones mentioned in this description as a starting point.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Farzon Lotfi (farzonl)

> These are the truncation tests we should support: > https://godbolt.org/z/73vj6jMs7 > > essentially if the src is bigger than the dest even if destination is a scalar we should truncate. this should be handled via a new `ICK_HLSL_Matrix_Truncation`. tha should behave similarly to `ICK_HLSL_Vector_Truncation` since they share the same spec. > > ```hlsl > export int3x3 trunc_cast(int4x4 i44) { > int3x3 i33 = (int3x3)i44; > return i33; > } > > export int3x2 trunc_cast2(int4x4 i44) { > int3x2 i32 = (int3x2)i44; > return i32; > } > > export int2x3 trunc_cast3(int4x4 i44) { > int2x3 i23 = (int2x3)i44; > return i23; > } > > export int2x2 trunc_cast4(int4x4 i44) { > int2x2 i22 = (int2x2)i44; > return i22; > } > > export int2x1 trunc_cast5(int4x4 i44) { > int2x1 i21 = (int2x1)i44; > return i21; > } > > export int trunc_cast6(int4x4 i44) { > int i21 = (int)i44; > return i21; > } > ```

Originally posted by @farzonl in #162711