Update web generation code to use NotoColorEmoji.
Update web generation code to use NotoColorEmoji.

These are small changes.

- ignore emoji/text presentation selectors when validating that a
  font can render all the text.  These are not in NotoColorEmoji
  but are in the sample emoji text. Variation selection processing
  strips them out, in our pipeline.  (They're still a problem for
  some pipelines).
- generate .png files if the font variant is 'color', NotoColorEmoji
  uses CBDT glyph image data and svg won't render it.  By default
  we use svg since it's more compact.
- tweak font size and line spacing to be a bit larger for the color
  emoji sample.

dougfelt/nototools,anthrotype/nototools,dougfelt/nototools,moyogo/nototools,moyogo/nototools,googlefonts/nototools,anthrotype/nototools,googlei18n/nototools,moyogo/nototools,googlefonts/nototools,googlei18n/nototools,googlefonts/nototools,googlei18n/nototools,dougfelt/nototools,googlefonts/nototools,googlefonts/nototools,anthrotype/nototools