FilteringGeneratorDelegate.writeUTF8String() should delegate to writeUTF8String()

[tlrx]

In its writeUTF8String() method, a FilteringGeneratorDelegate uses the delegating writeRawUTF8String() method that do not manage additional escaping:

@Override
public void writeUTF8String(byte[] text, int offset, int length) throws IOException
{
    // not exact match, but best we can do
    if (_checkRawValueWrite()) {
        delegate.writeRawUTF8String(text, offset, length);
    }
}

I think it should use the delegate.writeUTF8String() instead so that it correctly escapes required chars:

    // not exact match, but best we can do
    if (_checkRawValueWrite()) {
        delegate.writeUTF8String(text, offset, length);
    }

This pull request changes that and adds a small unit test.

[cowtowncoder]

Ah yes, good catch. Cut'n paste error. Thank you for reporting this!
I'll manually backport this in 2.7 as well.

[tlrx]

@cowtowncoder awesome, thanks!