fix(perf): Improve performance by converting patterns to regexp only once

[lo1tuma]

I’ve profiled a c8 mocha run against a huge test suite (5000+ tests) which spotted the minimatch call within shouldInstrument as a bottleneck. Since shouldInstrument is called quite often but the the exclude patterns don’t change over time a lot of CPU time is wasted parsing the same glob patterns again and again.
This change converts all glob pattern to regex patterns in the constructor, so this is only done once.
I’ve profiled the same run after applying those changes and minimatch is no longer the bottleneck, instead globSync() is the next bottleneck

[bcoe]

@lo1tuma thanks for this digging, seems smart to me to only create the regex once.

[bcoe]

@lo1tuma it looks like this has angered the Windows gods.