Add warnings to unsafe modules

Data/Text/Internal/Builder.hs

Data/Text/Internal/Builder/Functions.hs

Data/Text/Internal/Builder/Int/Digits.hs

Data/Text/Internal/Builder/RealFloat/Functions.hs

Data/Text/Internal/Encoding/Fusion.hs

Data/Text/Internal/Encoding/Fusion/Common.hs

Data/Text/Internal/Encoding/Utf16.hs

Data/Text/Internal/Encoding/Utf32.hs

Data/Text/Internal/Encoding/Utf8.hs

Data/Text/Internal/Functions.hs

Data/Text/Internal/Fusion.hs

Data/Text/Internal/Fusion/Common.hs

Data/Text/Internal/Fusion/Size.hs

Data/Text/Internal/Fusion/Types.hs

Data/Text/Internal/IO.hs

Data/Text/Internal/Lazy.hs

Data/Text/Internal/Lazy/Encoding/Fusion.hs

Data/Text/Internal/Lazy/Fusion.hs

Data/Text/Internal/Lazy/Search.hs

Data/Text/Internal/Unsafe.hs