docs: Reference functions instead of methods (#38986)

By referencing methods sometimes and not just functions, there was some duplication and confusion. For instance, we had `get(::Any, ::Any, ::Any)` method and also a `get` function, the latter of which duplicated the documentation for the former on the same page.

Author: BioTurboNick

doc/src/base/collections.md

@@ -200,10 +200,8 @@ Base.IdDict
 Base.WeakKeyDict
 Base.ImmutableDict
 Base.haskey
-Base.get(::Any, ::Any, ::Any)
 Base.get
-Base.get!(::Any, ::Any, ::Any)
-Base.get!(::Function, ::Any, ::Any)
+Base.get!
 Base.getkey
 Base.delete!
 Base.pop!(::Any, ::Any, ::Any)