This commit updates the management of the `may_enter` flag in line with
WebAssembly/component-model#57. Namely the `may_enter` flag is now
exclusively managed in the `canon lift` function (which is
`TypedFunc::call`) and is only unset after post-return completes
successfully. This implements semantics where if any trap happens for
any reason (lifting, lowering, execution, imports, etc) then the
instance is considered permanently poisoned and can no longer be
entered.
Tests needed many updates to create new instances where previously the
same instance was reused after it had an erroneous state.
e179e736b9