swaybar: use text subpixel antialias only where it would look good

Closes #5605

Text Subpixel antialiasing is :

- FreeType makes glyph bitmaps containing coverage percentage for each
  subpixel, instead of pixel
- Then draw by performing the blend for each subpixel, instead of pixel (e.g.
  dual-source blending in opengl)

And there's only one Alpha channel, so this extra coverage data can't
leave Cairo to reach the compositor through there.
Therefore, it can't work as intended if output text alpha != bar background
alpha. Disable it for those cases, enable it elsewhere

As for color emojis, they are RGBA bitmaps. If drawn with text alpha=1.0
and background alpha=1.0 (should be completely opaque bar), then with
'CAIRO_OPERATOR_SOURCE' then texels with alpha < 1.0 result in a blend with
whatever's behind the bar, instead of the bar background

0 files changed, 0 insertions, 0 deletions