Handle n:n relationships between glyphs and character input

[travisleithead]

From CG meeting on 8/18

Glyph relationships with respect to the source text is a many-to-many relationship. Graphemes not covered. This is a lot of complexity (especially for editing scenarios and caret movement logic). Consider simplifying and focusing on rendering needs only (e.g., size and position) if possible.

In most N-to-N mappings, knowing why they are mapped that way is important (Arabic decomposition different from emoji)