[perl #45667] Apply tests from #119125 in reverse

Ticket #119125 represents the breakage caused by c30fc27b4df65a, which
fixed #45667 (/[#]$not_interpolated/x; a regression from 5.000) as a
side-effect of fixing /[#](?{this is not a code block})/x (a regres-
sion from 5.16.0).

It was backported to maint-5.18, which broke several modules, because
bug #45667 is *old*, and many modules depend on it.

So 02682386fe3e on the maint branch modified the fix to apply only to
code blocks, and added tests to make sure that #45667 wasn’t fixed.

#45667 is fixed in blead, but is untested, so grab the tests from
02682386fe3e and reverse the logic of the second one.
perldelta: missing =item
perldelta for c30fc27

The first part was stolen from 72251ce78c061 on the maint-5.18 branch.
perldelta: anither to-do
perldelta for 1311cfc
perldelta for 3df32bd
perldelta for 6b35226
perldelta for 51da40e
perldelta: another to-do
perldelta for 649c173
perldelta for 9e0ea7f

The thing about locking hash keys inside the substitution and
vivifying globs is too hard to explain clearly and concisely.
This section is entitled ‘*Selected* Bug Fixes’, after all.
perldelta for a547fd2
perldelta: another to-do
perldelta for 3b68edc
perldelta for 48120f8
perldelta for 85b7d9b
perldelta for 9bcf803 and 376ccf8
perldelta for 5f213d9
perldelta for 045071e
Stop reset from clearing aliases to globs

If $z has been aliased to *foo, then reset("z") would turn off the
SvOK flags on *foo, putting it in an inconsistent state.  This could
cause crashes.