[TODO] fix #13528 nimgrep --word now works with operators

[timotheecour]

• fix [minor] nimgrep --word doesn't work with operators (eg misses 1 +% 2) #13528 nimgrep --word now works with operators
• uses same pattern as ripgrep instead of \b (thanks to @BurntSushi for the idea!)

caveat

Here's an edge case that could be considered a false positive depending on how you interpret --word, but it's a bit trickier o fix and definitely better than having false negatives

/Users/timothee/git_clone/nim/Nim_prs/tools/nimgrep --find -r --ext:nim --word '\$\$' lib
lib/pure/parseutils.nim:588:     for k, v in interpolatedFragments("  $this is ${an  example}  $$"):
lib/pure/marshal.nim:45: ## **Note**: The ``to`` and ``$$`` operations are available at compile-time!
lib/pure/marshal.nim:296: proc `$$`*[T](x: T): string =
lib/pure/strutils.nim:2709:   ## To produce a verbatim ``$``, use ``$$``.
lib/pure/strscans.nim:41: ``$$``              Matches a single dollar sign.
lib/pure/strscans.nim:693:   let xx = scanf("$abc", "$$$i", intval)
lib/pure/strscans.nim:697:   let xx2 = scanf("$1234", "$$$i", intval)
lib/pure/parsexml.nim:609:   # if we have no name, we have '<tag attr= key %&$$%':
lib/impure/nre.nim:713:   ## -  ``$$`` - literal ``$``
9 matches

ripgrep has same issue here:

echo 'let xx = scanf("$abc", "$$$i", intval)' | rg -w '\$\$'
let xx = scanf("$abc", "$$$i", intval)

TODO for future PR

• --word should add an extra check that filters out entries bcd preceded by a b or succeeded by a d; this would filter out $$$i in this case.
• ripgrep could use a similar trick /cc @BurntSushi