Report warning when loop variable shadows one from outer scope in HLSL 2021

Description
Prior to HLSL2021, a loop variable that shadowed one from the outer scope generated a warning. With HLSL 2021, that warning does not appear.

Steps to Reproduce

// RUN: %dxc -T ps_6_6 -HV 2021 %s

float4 main(float f: F) : SV_Target {

       uint i = 7;
       for (uint i = 0; i < 3; i++) {
         f += i;
       }
       return f + i;
}

produces:

 warning: redefinition of 'i' shadows declaration in the outer scope; most recent declaration will be used [-Wfor-redefinition]
       for (uint i = 0; i < 3; i++) {

Actual Behavior

with HLSL2021 enabled, no warning is produced.

Environment

• DXC version (dxcompiler.dll: 1.7 - 1.7.0.3942)
• Host Operating System Win11

Start by running the inline HLSL reproduction with DXC using -T ps_6_6 -HV 2021 and compare its behavior with the shown warning. Trace the compiler's handling of loop-variable shadowing for HLSL 2021; done means the reproduction emits the outer-scope shadowing warning again.