Code.Fragment.cursor_context/1 does not understand more complicated expressions

[lukaszsamson]

Environment

• Elixir & Erlang/OTP versions (elixir --version): 1.13, dev

Current behavior

this is OK

iex(1)> Code.Fragment.cursor_context("DateTime.utc_now()")   
:none

but this could be improved

iex(2)> Code.Fragment.cursor_context("DateTime.utc_now().")
:none
iex(3)> Code.Fragment.cursor_context("DateTime.utc_now().ho")
:none

Expected behavior

It would be great if the return value was {:dot, {:dot_call, ..., ...}, ...} or {:dot, :expr, ...}.

[josevalim]

This requires adding new return types, so we will move it out of v1.14 for now.