Suggest supplier when typing a period after a function name

[MeAmAnUsername]

Summary
Suggest supplier when typing a period after a function name

Todo

• Figure out how to show suggestions in Spoofax: Suggestions in the editor #271
• Implement

Example
Given

func foo(x: int) -> unit = {}
func use() -> unit = foo

If the user types . at the end (after foo) so it becomes foo., suggest foo.supplier($Exp)

Description
Only show suggestion while the user is typing any part of .supplier(, not when just moving the cursor with the arrow keys.
Only show on function names where an expression is expected.
Also show if identifier could be either a function name or a value. In that case, show suggestions for both supplier of function (this issue) or for methods on the data type ([todo: create issue for suggestions for methods], #82).
Number of placeholder arguments matches the number of parameters of the function.
Also show even when a supplier would lead to type errors (there is nothing else a user could intend when typing . after a function name.

Related issues

• General issue for suggestions (prerequisite for this issue): Suggestions in the editor #271
• Suggest method call for data types: Use period after expression to get function suggestions #82, [todo: to be created]