Handle soft hyphens

[DJMcNab]

These are treated as an in-word line breaking opportunity (possibly uniquely without breaking kerning?) but not as a visual space.
If the line breaking opportunity is taken, they're rendered as a hyphen.

Currently we treat these as a line breaking opportunity, but don't render the hyphen (I believe).

[xorgy]

Also one thing to note is that soft hyphen can have a distinct glyph from hyphen-minus, and I believe there are fonts which use this (e.g curved right terminal on soft hyphen).

[DJMcNab]

I was under the impression that it uses hyphen (U+2010) rather than hyphen minus.

I don't believe at least Chrome uses the actual cmap entry for soft hyphen directly (even though I do know of at least one font which has that, U+2010 and U+002D mapped and with different content!)

[behdad]

I don't believe at least Chrome uses the actual cmap entry for soft hyphen directly

Correct. HarfBuzz eats soft-hyphen.