Switch BUnicodeChar to wrap the ICU's UChar32 one

Improve the unicode character processing and classifying routines by
wrapping up the UChar32 procedures from ICU. That fixes functional
regression introduced in hrev38017 and allows to fix East Asian Width
problems int the Temrinal.
Fix support of East Asian Full Width characters

* Re-enable full-width characters detection and display;
* Fix cursor drawing on full-width characters;
* Fix debug dump for multi-byte characters;
* Fix file permissions for debug capture log.

Fixes #6717. Also may improve behaviour related to #6227.
Don't call DrawExpanderArrow() directly, set a variable and Invalidate()
Also nullify other saved items on delete
Remove dead code