Preserve precise exceptions in strictness analysis

Fix #13380 (closed) and #17676 (closed) by

1. Changing raiseIO# to have topDiv instead of botDiv
2. Give it special treatment in Simplifier.Util.mkArgInfo, treating it as if it still had botDiv, to recover dead code elimination.

This is the first commit of the plan outlined in !2525 (comment 260886).