JIT: Fix Lowering::LowerRange

[jakobbotsch]

For example, this would break when LowerNode ended up deciding to remove the current node.

To make this fully robust we now insert a sentinel node and stop when we get to it. Using lastNode->gtNext as the sentinel node would seemingly be possible, but we have code that removes the user of the node being lowered, which would not work in that scenario:

runtime/src/coreclr/jit/lowerxarch.cpp

Lines 1506 to 1514 in 78142b0

	LIR::Use superUse;
	if (BlockRange().TryGetUse(user, &superUse))
	{
	superUse.ReplaceWith(op2);
	}
	else
	{
	op2->SetUnusedValue();
	}

.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.