The current description (especially the "unlimited width" part) is
inaccurate in several ways:
- The size of virtual text can depend on window width. In particular,
the size of "above" virtual text can be equal to window width.
- A double-width character that doesn't fit adds 1 to the virtual column
of the following characters.
- The size of 'showbreak' and 'breakindent' is counted.
related: vim/vim#5713closes: vim/vim#18447014c731fa5
(cherry picked from commit 43f7434bd5)
dd79bc8360