Tracking issue: Features for Blitz

[nicoburns]

This issue tracks features that Blitz needs from Parley

Bugs fixes

• Misc. inline box layout fixes #207

Fontique

• Webfonts: Ability to customise name and attributes used for matching when loading a font (initial functionality implemented in Add APIs for overriding fonts' metadata at registration time and unregistering fonts #312)
• Webfonts: The ability to remove/unload fonts
• More easily reuse system-fonts across collections (currently only possible by cloning the FontCollection)

Parley features

• Inline boxes
• Tree-based styles
• Production grade shaping
• Whitespace collapsing
• Hit testing for inline spans (Add external span IDs #230)
• word-break style (Implement word-break and overflow-wrap style properties #315)
• overflow-wrap style (Implement word-break and overflow-wrap style properties #315)
• text-wrap-mode style (Add TextWrapMode style #367)
• vertical-align style (Vertical alignment and the concept of a "parent" font and style #291)
  • Baseline alignment for inline boxes
  • Subscript and superscript
• Floated boxes (CSS Floats) #99
• Overflow handling:
  • text-overflow (horizontal overflow)
  • line-clamp (vertical overflow)
• white-space-collapse style
• white-space-trim style
• Small caps (text-transform)
• Bounding boxes for inline spans
• Margin/border/padding for inline spans (should be bidi-aware)
• BiDi-direction overrides (html dir attribute)
  • Root-level default BiDi direction
  • Span-level overrides of BiDi direction