Docs: UTF-8 character can take up 4 bytes

[ChrisGreenaway]

Elasticsearch version (bin/elasticsearch --version): master

Plugins installed: N/A

JVM version (java -version): N/A

OS version (uname -a if on a Unix-like system): N/A

Description of the problem including expected versus actual behavior:

ignore-above.asciidoc says "If you use UTF-8 text with many non-ASCII characters, you may want to set the limit to 32766 / 3 = 10922 since UTF-8 characters may occupy at most 3 bytes." however a UTF-8 character can take up 4 bytes.

Steps to reproduce:

Look at ignore-above.asciidoc

Provide logs (if relevant):

[nik9000]

@clintongormley git blame says you wrote this. @ChrisGreenaway is right, 4 bytes is possible, but not common. It looks like 4 bytes is fairly rare unless you are dealing with fairly special text. Or emoji.

[DaveCTurner]

I agree - pretty common to see emoji these days. I opened #27083.

[DaveCTurner]

Thanks for the report, @ChrisGreenaway, much appreciated.

[ChrisGreenaway]

You are welcome. Thanks for fixing it.