Changes to match NQP qast_refactor branch.
Add a few typed exceptions and override P6Regex::Grammar methods to throw them.

This lets us test sensibly for RT #77380, RT #77522 and similar.
A few changes needed by qast_restructure in NQP.

Only one known regressions remains, which is related to compile-time
inlining of multis.
teach clone_qast (and thus node_walker) about QAST::Children
Toss clone_qast sub; there's a method for that.
Fix is_clearly_returnless for empty block case.

Not sure how this ever really worked out in the past; perhaps a
QAST tree mis-construction that's now impossible made it appear
to work.
Bump NQP_REVISION to for restructured QAST nodes.
Merge branch 'qast_refactor' into nom
Revert "Merge branch 'qast_refactor' into nom"

This reverts commit 54cde6bfd1dd23bd7998334b602183e1ee134b31, reversing
changes made to 356d57aabbc54eb2d6030236ebdff02ebe992335.
Merge branch 'qast_restructure' into nom
In UNIT, no need for wasteful clone operations.

There's only ever going to be one anyway, since it's in UNIT. Avoids
a little work at startup and saves us some allocations, memory, etc.
Fix for RT #79160
Get Date from Instant (RT #111356)
Bump NQP_REVISION; use new .code_object support.
Merge pull request #301 from peschwa/panics_to_typeds

Add a few typed exceptions and override P6Regex::Grammar methods to throw them.