Move __builtin_hlsl_wave_get_lane_index to EmitHLSLBuiltinExpr

[farzonl]

Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID, const CallExpr *E)

is where all the other hlsl builtins live.

Originally posted by @farzonl in #80680 (comment)

[marcauberer]

I can do that

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Farzon Lotfi (farzonl)

`Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID, const CallExpr *E)`

is where all the other hlsl builtins live.

Originally posted by @farzonl in #80680 (comment)