* Remove padding values in line_heights and glyph_position_x. Each value
in glyph_position_x now represents an actual glyph in the layout.
* Remove code intended to handle extra characters beyond the end of the
last line. The LineBreaker should ensure that the end of the last run
matches the end of the last line.
* Return the upstream/downstream affinity of the cursor position in
GetGlyphPositionAtCoordinate.
* Account for the space at the end of a word wrapped line in
GetGlyphPositionAtCoordinate / GetCoordinatesForGlyphPosition
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