At present, `var *;` is a crash because it has errors that weren't being properly stored/handled. This changes the handling to give more to track invalid parses in patterns.
This changes `return`, `break`, and `continue` to treat the keyword as the "start" and semicolon as the "parent", essentially bracketing the keyword.
Pragmatically this is focusing on making `return` work with only one ParseNodeKind: because `return` and `;` now bracket the expression, we can tightly determine whether the `return` has arguments without looking at subtree size. However, it's possible that `break` and `continue` may in the future take some kind of label as an argument, so the consistency seems beneficial there too.
Note this eliminates the StatementEnd ParseNodeKind, as it's obsolete with this change.
Jon Ross-Perkins