[protocol] Add range information to DocumentDiagnosticParams

As discussed in https://github.com/microsoft/language-server-protocol/issues/737#issuecomment-1287302940 and https://github.com/microsoft/language-server-protocol/issues/718#issuecomment-1206503252 , for some languages computing diagnostics can be quite expensive.

In such cases, it'd be very convenient for the Pull Diagnostics request to provide a range parameter, so the server can opt to compute diagnostics for the relevant part of the file that is in view of the user.

That is only meant to be a hint, and servers should be free to ignore it.

I understand that this change together with the current support for Pull Diagnostics would be enough to implement a reasonable "check on scroll" functionality which a few IDEs in the context of theorem proving support.

c.f. #1414

Start with the DocumentDiagnosticParams definition and the Pull Diagnostics request in the protocol specification, then read the linked discussions and issue #1414. Determine how a range hint should be represented and documented while preserving servers’ ability to ignore it. Done means the protocol clearly defines the optional range behavior and its compatibility implications.