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MFC r317665: bsdgrep: fix -w -v matching improperly with certain patterns

-w and -v flag matching was mostly functional but had some minor
problems:

1. -w flag processing only allowed one iteration through pattern
   matching on a line. This was problematic if one pattern could match
   more than once, or if there were multiple patterns and the earliest/
   longest match was not the most ideal, and

2. Previous work "fixed" things to not further process a line if the
   first iteration through patterns produced no matches. This is clearly
   wrong if we're dealing with the more restrictive -w matching.

#2 breakage could have also occurred before recent broad rewrites, but
it would be more arbitrary based on input patterns as to whether or not
it actually affected things.

Fix both of these by forcing a retry of the patterns after advancing
just past the start of the first match if we're doing more restrictive
-w matching and we didn't get any hits to start with. Also move -v flag
processing outside of the loop so that we have a greater change to match
in the more restrictive cases. This wasn't strictly wrong, but it could
be a little more error prone.

While here, introduce some regressions tests for this behavior and fix
some excessive wrapping nearby that hindered readability. GNU grep
passes these new tests.

PR:             218467, 218811
Approved by:    emaste (mentor, blanket MFC)

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