Add a quick watch popup for easy debugging of expressions

[filipdutescu]

Description

A common feature in modern IDEs, which is very useful for quick evaluations of expression, without the need to add (and most likely edit and delete) a watch is quick watch (or evaluate). It shows the values of expressions using the current scope as a context for variables, functions etc.

Proposal

Add a quick watch popup, which could start empty or from the current code selection, behaving similar to a picker, with expandable values for the result of the expression. Expandable values should follow the implementation of locals from #5954.

UI mockups

[pascalkuthe]

I belive #5768 also contains a similar overlay tree view in addition to the side tree view so again basing your work on that pr will help

[filipdutescu]

Yep, will do so, this change will probably depend on #5954, since after that one this one will probably be relatively trivial to achieve.