regex: special case literal extraction
regex: special case literal extraction

In a prior commit, we fixed a performance problem with the -w flag by
doing a little extra work to extract literals. It turns out that using
literals in this case when the -w flag is NOT used results in a
performance regression. The reasoning is that we end up using a "fast"
regex as a prefilter when the regex engine itself uses its own
equivalent prefilter, so ripgrep ends up redoing a fair amount of work.

Instead, we only do this extra work when we know the -w flag is enabled.

BurntSushi/ripgrep,BurntSushi/ripgrep,BurntSushi/ripgrep,BurntSushi/ripgrep