Implement a generic topological sort algorithm

recursive-patterns(5): Respond to code review comments in #23208 and #23209, #23228, and #23357

recursive-patterns(4): Parsing the switch expression.

recursive-patterns(3): Implement the decision DAG and subsumption checking.

Improve handling of array builder in in LocalRewriter.LowerIsPattern

recursive-patterns(2): Add support for recursive patterns in `is`

Fixes #22969

Size array builders at creation time.
Eliminate more uses of `var` in place of explicit types.
Use Hash.Combine

Replace "TODO(patterns2)" with "PROTOTYPE(patterns2)"

Merge features/compiler into features/recursive-patterns