[mlir][async] Erase op later to preserve insertion point (llvm#146516)

Delay the erasure of an op, so that the insertion point of the rewriter remains valid. This commit is in preparation of the One-Shot Dialect Conversion refactoring. (The current implementation works with the current dialect conversion driver because op erasure is delayed.)

Author: matthias-springer

mlir/lib/Dialect/Async/Transforms/AsyncToAsyncRuntime.cpp

@@ -723,8 +723,8 @@ class YieldOpLowering : public OpConversionPattern<async::YieldOp> {
  // Switch the coroutine completion token to available state.
  rewriter.create<RuntimeSetAvailableOp>(loc, *coro.asyncToken);
 
- rewriter.eraseOp(op);
  rewriter.create<cf::BranchOp>(loc, coro.cleanup);
+ rewriter.eraseOp(op);
 
  return success();
  }