add scaladoc note to Unicode unaware methods
add scaladoc note to Unicode unaware methods

Some methods in StringOps are unicode unaware and likely to
return invalid strings if they are used without keeping
surrogate pair handling in mind. These were previously
deprecated, but were undeprecated again because they are
useful in various contexts where unicode handling is not
required.

lrytz/scala,scala/scala,lrytz/scala,scala/scala,scala/scala,scala/scala,scala/scala,lrytz/scala,lrytz/scala,lrytz/scala,lrytz/scala,scala/scala