add `drracket:define-popup` configuration to `#lang`-based `get-info`

[mflatt]

This change allows Rhombus to configure DrRacket so that the (define ...) menu becomes a def menu that jumps to Rhombus definitions.

Besides allowing #lang-based configuration, the change refines how the definition popup works:

• Instead of looking for Scheme-style comments, recognize text that should not match based on its syntax-coloring category, ignoring would-be matches in comments or in string literals.

• Allow the configuration to specify case-sensitive matching and delimited matching, where the definition of "delimited" is derived from the expression-navigation configuration.

[mflatt]

Updated with test repairs, thanks to Robby.

[rfindler]

I've pushed a commit here that tries changes one part of the strategy of this change. Instead of having unit.rkt having stuff that's module-language specific, I've adjusted the plumbing related to capability-value so it always has access to the irl. Then that part of this change is a bit simpler and cleaner and it should also be easier if we want to migrate more of the stuff currently into capability-value into #lang-specific customizations.

[rfindler]

I've squashed these commits and pushed to master: https://github.com/racket/drracket/commit/fc48296eef63dee1f301a3d1da54456e97283557

[racket-discourse-github-bot]

This pull request has been mentioned on Racket Discussions. There might be relevant details there:

https://racket.discourse.group/t/what-are-some-benefits-that-rhombus-development-has-brought-to-racket/2054/1