* Include `DeclContext` of the node where possible
* Add 'default-with-decl-contexts' dump style that dumps the dect context
hierarchy in addition to the AST
* Support `-dump-parse` with `-dump-ast-format json`
A `let` binding of a copyable subpattern can create an independent variable
which should be copyable and consumable without affecting a borrowed
move-only base. In the same way that `borrowing` parameters are
no-implicit-copy, though, explicitly `_borrowing` subpatterns of
copyable type should be no-implicit-copy as well.
When matching against a noncopyable value, whether the match operation can
borrow the value in-place or needs to take ownership of it is significant.
This can generally be determined from the kind of pattern being used, except
in the case of expr patterns, where it depends on type-checking the `~=`
operator that was used.
