Puppet::Util::Warnings#maybe_log potentially very slow

https://github.com/puppetlabs/puppet/blob/293b87447ff955bb4c866b5b0eda3a23e5901ff2/lib/puppet/util/warnings.rb#L23-L30

Puppet::Util::Warnings#maybe_log stores the list of messages that it has logged from each class in an array, and uses Array#include? to see whether the message has already been seen. This has the potential to slow down significantly as the number of messages logged from a specific class increases.

We should probably look into storing the set of previously seen messages in something with a lookup time closer to O(1) than the current O(N) scan through the array.