Hovering for implicit behavior in the grammar language

[msujew]

Stuff like

• Which token/data type rule is used for cross references
• TypeScript type definitions for types built from parser rules

[danieldietrich]

For cross-references (in my mental model I see them as inline rules) like func=[type:alternative], we can omit the alternative. What remains is func=[type] and Langium implicitly adds the alternative. Here, it would be helpful to have a link in the tooltip that navigates to the origin of the implicit information.

Example:

Rule: func=[AbstractFunc]

// The tooltip shows the following when hovering AbstractFunc:
// AbstractFunc: ID (inferred from Xxx)
//                                 ^^^---- link to the 'name' attribute of a rule (or type?) that led to ID

[spoenemann]

See also #450