Add support for denotation by tree

[ShaneDelmore]

A common request is to get the denotation of a tree. As a rough guess this would be the denotation of the last element in the tree unless it is a block, in which case it would be the denotation of the last statement in the block.

[xeno-by]

Can you give an example?

[olafurpg]

If I understand correctly, this sounds like Term.tpe which will require https://github.com/scalameta/scalameta/issues?q=is%3Aissue+is%3Aopen+label%3ASymtab

[ShaneDelmore]

@olafurpg What is the current proper usage of index.denotation(tree)? This came up as the last couple of times I have paired with people working with scalameta and scalafix this is a thing that frequently looks useful based on type signatures, but always results in None. I might be misunderstanding when I should be looking for denotation vs tpe

[olafurpg]

that method is a shorthand for denotation(symbol(tree)), it should return results for refs (a, a.b) etc but more complex expressions it's expected to return none

[olafurpg]

Duplicate of #1212. You can query the type of a symbol with the current api but not a term.