[MLIR] Prevent invalid IR from being passed outside of RemoveDeadValues (#121079)

This is a follow-up for #119110
and a fix for #118450

RemoveDeadValues used to delete Values and analyzing the IR at the same
time, because of that, `isMemoryEffectFree` got invalid IR with
half-deleted linalg.generic operation. This PR separates analysis and
cleanup to prevent such situation.

Thank you!

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Co-authored-by: Renat Idrisov <parsifal-47@users.noreply.github.com>
Co-authored-by: Andrzej Warzyński <andrzej.warzynski@gmail.com>

Author: parsifal-47