Standardize on Python `match`/`case`-style blocks

[evhub]

Should deprecate case/cases blocks with match statements inside of them in favor the Python-style match block with case statements inside of it. However, since this is inconsistent with the stand-alone match <pat> in <it> statement that puts the pattern after the match keyword, we'll also want to add a new stand-alone match statement that puts the item to be matched against after the match keyword like the Python syntax. For that, the proposed syntax is:

match <item> with <pattern>:
    ...

[evhub]

case/match syntax is now deprecated in favor of match/case or cases/match syntax. Unsure whether match ... with syntax makes sense to add or not; seems like supporting it alongside match ... in syntax could be quite confusing.