Only the first range is styled in discontinuous selections

All ranges in a discontinuous selection should have a style applied.

to reproduce:
1. Select, using the cmd key, a number of different words from a paragraph.
2. Make the text bold by selecting **Format > Strong** or **cmd-B** keyboard shortcut.
3. Only the first word is styled bold.

Start by reproducing the issue in MacDown with a discontinuous selection, then trace the Format > Strong action and cmd-B shortcut handling. Done means every selected word or range is styled bold rather than only the first.

Written by the indexing model from the issue text.