Share route pattern parsing logic between analyzers and generators

Both the route handler analyzers and the RequestDelegateGenerator share a requirement for being able to parse a route pattern string and extract information about the route parameters in it, constraints on those parameters, etc.

We should identify a way to share this code across the analyzers and generators.

As part of consuming this logic in the RequestDelegateGenerator we want to emit logic that will determine if a parameter appears in the route and sourcing it from the route values dictionary.

cc: @halter73 as this relates to the parameter binding work
cc: @JamesNK who has knowledge in this area