Investigate support of surrogate pairs in all text processing

According to PIVOT-850, most if not all the code that advances through text (such as for label sizing, drawing, etc.) uses CharSequence to do so (usually using "charAt()" method).  This does not work correctly for surrogate pairs (such as emoji).  And maybe the TextLayout stuff used by IME support needs tweaking as well....

This issue is meant to collect all the fixes / changes necessary so that emoji (or any surrogate pair characters) will work with all the Pivot text code.