Use moveToCodepointOffset for cursor routing (#16477)
Fixes #10960
Summary of the issue:
There are cases where moving one character on a textInfo instance actually moves more than one unicode point offset. This is described by @mltony in the doc string for textInfos.TextInfo.moveToCodepointOffset.
This causes of by one errors when cursor routing, since we're asking the textInfo to move by 1 characters, that might be presented by two or even more characters within the liblouis mapping.
Description of user facing changes
Cursor routing should be more reliable.
Description of development approach
@mltony's creation of moveToCodepointOffset allows us to move x code points from the start of the reading unit. As we're using 32 bit for liblouis, every character as presented by liblouis is equal to one code point. Therefore we can safely assume that this method to move is much more reliable than the previous method.
