edits after a wide characters can get out of sync

[jvasileff]

Testing with 𝐙 ({#01D419}), and starting with:

shared void run() {
    print("𝐙");
}

typing code after the print statement results in an error:

shared void run() {
    print("𝐙"); print("edit");
}

[jvasileff]

See microsoft/language-server-protocol#19 for the definition of a character.

[jvasileff]

The LSP now specifies that offsets are in 16-bit code units, whereas Ceylon's characters are 32-bit code points. So the text replacement code should probably use java.lang.String rather than ceylon.language::String.