Add missing listener notifications when erasing nested
blocks/operations.
This commit also moves some of the functionality from
`ConversionPatternRewriter` to `ConversionPatternRewriterImpl`. This is
in preparation of the One-Shot Dialect Conversion refactoring: The
implementations in `ConversionPatternRewriter` should be as simple as
possible, so that a switch between "rollback allowed" and "rollback not
allowed" can be inserted at that level. (In the latter case,
`ConversionPatternRewriterImpl` can be bypassed to some degree, and
`PatternRewriter::eraseBlock` etc. can be used.)
Depends on #145018.
0921bfd81d