[5.7] Fix algorithms overload resolution issues

[natecook1000]

This change addresses two overload resolution problems with the
collection-based algorithm methods. First, when RegexBuilder is
imported, String gains RegexComponent conformance, which means
the RegexComponent-based overloads win for strings, which is
undesirable. Second, if a collection has an element type that can
be expressed as an array literal, collection-based methods get
selected ahead of any standard library counterpart. These two problems
combine in a tricky way for split and contains.

For split, both the collection-based and regex-based versions need
to be marked as @_disfavoredOverload so that the problems above can
be resolved. Unfortunately, this sets up an ambiguity once String
has RegexComponent conformance, so the RegexBuilder module
includes separate overloads for String and Substring that act
as tie-breakers. If introduced in the standard library, these would
be a source-breaking change, as they would win over the Element-
based split when referencing the split method, as with
let splitFunction = myString.split.

For contains, the same requirements hold, with the added
complication that the Foundation overlay defines its own
String.contains(_:) method with different behavior than included
in these additions. For this reason, the more specific overloads for
String and Substring can't live in the RegexBuilder module,
which creates a problem for source compatibility. As it stands now,
this existing code does not compile with the new algorithm methods
added, as the type of vowelPredicate changes from (Character) -> Bool to (String) -> Bool:

let str = "abcde"
let vowelPredicate = "aeiou".contains
print(str.filter(vowelPredicate))

[natecook1000]

@swift-ci Please test