Consider support extracting information from `#{{template}}`

More specifically, I find myself sometimes wanting to define a regex as the argument and extracting that string for whatever purpose.

Something like #{{foo.bar}} might invoke 'foo.(.*)'

It may be necessary to add a parameter to the arguments to support this context.

I think this could also let us separate the import lookup (#6) and the templating into separate components.
#{{riverpod|Provider}} would invoke '(.*)|(.*)', which would call to the import handler.

Might be saner to have it accept a Pattern to preserve existing functionality, modulo that extra parameters, or we could have a second args parameter like patterns: {RegEx('...'): (match) {...}}

More of an idle thought right now, but it may be worth considering.

No files, tests, or entry points are named; begin by locating the existing template and import-lookup handling in the Dart package. Clarify whether regex extraction, Pattern arguments, or a separate patterns argument is wanted, then define the behavior for examples such as #{{foo.bar}} and #{{riverpod|Provider}} before implementation.