[core] Add computed text ranges

[szabototo89]

Regular TextRanges are very expensive. In that cases where text ranges value can be predicted should use computed text ranges. For example:

{ "name": "John Doe" }
where "name" is the whole text range in KeyDeclaration

In the previous case we shouldn't create a new text range just for getting its "pure" value (name itself), but we know exactly that "name" is computed from name and two other quotes. It is easy to calculate.