Implements the strong mode proposal's restrictions on the behaviour of the
delete operator for strong objects.

Setting the strong bit is still wip, so this change will only affect those
objects that have the bit correctly set. The tests reflect this, and will be
expanded as more objects can be marked as strong.

Attempt 2, last version did not work with API.

BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1156573002

Cr-Commit-Position: refs/heads/master@{#28724}