[llvm] [DAG] Remove OneUse restriction on sext when folding (shl (sext (add_nsw x, c1)), c2) (PR #68972)

[via llvm-commits]

LiqinWeng wrote:

> Are you intending to abandon this for #69105?

I found test of X86/pr65895.ll , llc -mtriple=riscv64 pr65895.ll , also regression(an extra register is used😂)；
this patch #69105， i will abandon；

https://github.com/llvm/llvm-project/pull/68972