Mitchell Hashimoto 1907c58972 renderer: consider powerline box glyphs whitespace for PUA scaling
This adds to the heuristics introduced for #1071. Please read that issue
and associated PRs in their entirety to understand this commit.

This extends our concept of "whitespace" to include powerline box
glyphs. We don't want to constrain nerd symbols next to powerline box
glyphs because box glyphs are often used to style and contain nerd
glyphs. For example, its common to see a right-facing semi-circle, then
a nerd font glyph, then a left-facing semi-circle to create a
pill-shaped label.

This allows those nerd font symbols to be rendered full size. Test
script below (copy the bytes):

    printf "󰃰\n"
    printf "󰃰 \n"
    printf "󰃰\n"
2024-01-25 15:35:48 -08:00
..
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2024-01-04 13:30:34 +01:00
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