BiDi: Right-align RTL glyphs
We render each glyph aligned to the top left corner of its cell. It doesn't matter as long as the font is really monospace.
There are often glyphs that are wider, e.g. emojis and special symbols, but potentially letters too. Currently they can overflow to the next cell in LTR context, and to the logically previous (that is: to the right) cell in RTL context.
Characters that have an RTL resolved direction should be aligned to the top right corner of their desired cells, so that if they overflow, they overflow to the left (i.e. towards the next character, just like in LTR).