[RISCV] Fix coalesced vsetvli's AVL LiveInterval not always being shrunk (#98286) Most of the time when we coalesce and delete a vsetvli, we shrink the LiveInterval of its AVL register now that there is one less use. However there's one edge case we were missing where if we have two vsetvlis with no users of vl or vtype in between, we coalesced a vsetvli without shrinking it's AVL. This fixes it by shrinking the LiveInterval whenever we delete a vsetvli, and also makes the LiveIntervals consistent in-situ by not removing the use before shrinking. This fixes a -verify-machineinstrs assertion in an MIR test case I found while investigating https://github.com/llvm/llvm-project/pull/97264#issuecomment-2218036877. I couldn't recreate this at the LLVM IR level, seemingly because RISCVInsertVSETVLI will just avoid inserting extra vsetvlis that don't need coalesced.
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