HFIR disagrees with bytecode on 8 of 35 held-out v3 programs #159

From Motoko's #154 review. This is also on base. x10 and x11 fail to compile under HFIR, x02 gets a runtime type error, x03 gets a false capability denial inside its grant, and x07, x08, x15 and x27 also differ. Related: #155. The v3 verifier doesn't use HFIR, so no v3 result is affected. Add HFIR to the v3 verifier once it's fixed.

Nits from the same review:

• A missing middle key in a nested get throws a type error; make it return nil or document it.
• Mixed-type nested rec literals are rejected at check time.
• pluck, select, group_by and merge should be marked experimental until a frozen set measures them.
• The report should note that put went unused, and say the forms were committed before the v3 solutions, not proven blind.