Display constraint in hover separately from real type

[radeksimko]

Background

As discovered in hashicorp/hcl-lang#326 there is increasingly more situations where the constraints and real types (as implied from values) mismatch, even if they're compatible.

For example, nested expressions in TemplateExpr - attr = "foo-${var.bar}" - where var.bar may be of type number but is constrained by the outer template expression to string.

Currently we choose to display the real type in that specific context, i.e. number:

similarly for ConditionalExpr, the condition part is constrained to bool but string is convertible to bool:

In general, one type will always communicate only "half of the story" and it is very likely there are other contexts where constraint may be more helpful than the real type.

Proposal

Display both the surrounding constraint and real type of an expression in hover data. We could display it at all times but it may be better to only do it when the two differ as that makes for more meaningful UX.