In a later PR more shape_cast ops will appear. Specifically, broadcasts that
just prepend ones become shape_cast ops (i.e. volume preserving broadcasts
are canonicalized to shape_casts). This PR ensures that broadcast-like
shape_cast ops fold at least as well as broadcast ops.
This is done by modifying patterns that target broadcast ops, to target
'broadcast-like' ops. No new patterns are added, the patterns that exist
are just made to match on shape_casts where appropriate.
This PR also includes minor code simplifications: use
`isBroadcastableTo` to simplify `ExtractOpFromBroadcast` and simplify
how broadcast dims are detected in `foldExtractFromBroadcast`. These are
NFC.
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Co-authored-by: Andrzej Warzyński <andrzej.warzynski@gmail.com>
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