Duplicated methods from implicit conversions in completions

[tgodzik]

Compiler version

3.6.3

Minimized code

Array(1,2,3).fil@@

Output

Multiple filter methods with the same signature.

Expectation

Single filter and filterNot method

First tackled in #14036

[rochala]

I tried fixing this issue some time ago.
As far as I remember, my approach was to adjust implicit search to not search all implicits:
val conversions = new typer.ImplicitSearch(defn.AnyType, qual, pos.span).allImplicits

But rather, actually find the best implicit:
1.isFini one coming from RichInt and the latter from RichLong
I did not not have much of success though