fix(NODE-3150): allow retrieving PCRE-style RegExp

[andymina]

Description

• Allowed retrieving PCRE-style RegExp by adding bsonRegExp option to commands, collections, and dbs
• Added unit tests for the bsonRegExp option

[durran]

I noticed our BSON library has this option to deserialize to the native RegExp or our BSONRegExp type, which to me is unexpected. We ran into this type of issue years ago in the Ruby driver, and the way we handled it there was to always deserialize to the BSON type, and if the user wanted the native type we added a compile method to it for them to get the native one. This seems a bit more intuitive to me than having to supply the option everywhere. @nbbeeken Maybe you have some context on why the BSON library is doing this? For reference https://github.com/mongodb/bson-ruby/blob/master/lib/bson/regexp.rb

Also to note is that the Java BSON library also behaves in the same way as Ruby, so that may be common across more drivers as well.

[nbbeeken]

I don't have further background on this, we have a precedent of other values being auto converted with the promoteValues and like settings. However, I know it is a strict requirement that BSON libraries have an API that explicitly converts UUIDs to native types, so that is a precedence for the opposite (as well as the regex examples from other libs you mention). There is convenience in handing the user the native type, up until it fails because of the contents.

Maybe as a separate effort we should take a look at the BSON library catching a Regexp decoding error and using BSONRegex automatically instead of failing, although I imagine that would also need a flag.

[durran]

Yeah it's a weird one since it is backwards breaking anyways so I guess we are stuck with a flag. Thanks for the clarification.

[durran]

I would also change the description not to mention findOne specifically, as the option is set on the command response before deserialization, which will actually take care of all commands (not just findOne).

[nbbeeken]

Some test clean up requests, driver changes LGTM

[nbbeeken]

We should use a better db/collection name here

[durran]

I'm LGTM once @nbbeeken 's test change requests are in.

[dariakp]

LGTM

[emadum]

LGTM