Check for interrupts during non-fast-update GIN insertion

Check for interrupts during non-fast-update GIN insertion

ginExtractEntries() can produce a lot of entries for a single item.
During index build, we check for interrupts between entries, and the
fast-update codepath does it as part of vacuum_delay_point(), but the
non-fast update insertion codepath was uninterruptible. Add
CHECK_FOR_INTERRUPTS() between entries in the non-fast update codepath
too.

Author: Vinod Sridharan <vsridh90@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAFMdLD6mQvAuStiOGvBJxAEfo6wdjZhj3+JveTLxOX8MVn4zmA@mail.gmail.com