More granular query for keyboard enhancement protocol support

[Iorvethe]

Is your feature request related to a problem? Please describe.
Some terminals could only support a subset of the keyboard enhancement protocol, but crossterm’s query for support only returns a boolean. This could be an issue when an application receives a positive answer for support, but the terminal doesn’t implement the entire protocol it expects (because of a work-in-progress or else). This issue was recently raised in Zellij (see zellij-org/zellij#3789).

Describe the solution you'd like
The proposed solution by Zellij’s maintainer was to either improve the current supports_keyboard_enhancement function or to add an additional interface for a more granular query. The second would be probably better, in my opinion, to avoid breaking existing code, but the semantics of the current function should be changed to mean a complete support of the protocol.

Describe alternatives you've considered if any
Complete implementation of the protocol by terminals, but this could not always be guaranteed, needed or wanted.