doesAnyCharRequireEscaping() conflicts with UTF-8

[janhec]

toStyledString() produces \u escapes for UTF-8 characters such as ï. This is caused by escaping on the ground that c > 0x7F in doesAnyCharRequireEscaping(), called from valueToQuotedStringN() from BuiltStyledStreamWriter::writeValue(). The last part of the condition imo should be removed; After removing c > 0x7F, I get normal UTF-8 which I need and is imo in line with the specs.