Add @Stable to java.lang.CharacterDataLatin1 and other CharacterData classes

[Claes Redestad]

> On second thought, we should just focus on adding stable and final as you recommend - we should fix stylistic things with no semantic impact later.

I’ll note that the code generator used to emit these CharacterData classes — build.tools.generatecharacter.GenerateCharacter — has legacy support to emit both Java and C code. This explain the choice to emit C-style arrays as a deliberate choice to simplify the code generator logic. 

I can’t find any use of this -c flag in our build or elsewhere though, so perhaps a little bit of clean up is in order.