Important changes:
* Change base class of nsRuby{Base,Text}Frame to nsInlineFrame
* Make ComputeSize of nsRubyFrame and nsRubyBaseContainerFrame behavior like inline frames
To account for spacing between bases or text boxes during reflow, the line
layout which manages the bases updates its inline direction coordinate based on
the preferred inline size for the corresponding text boxes. Next, the base is
reflowed at the correct inline coordinate. Each paired text box is then also
reflowed at the proper inline position determined by (1) the current position of
its corresponding base and (2) its own preferred width.
In computing intrinsic widths, accounting for spacing is less complicated. The
minimum intrinsic width is the width of the widest ruby column, and the
preferred intrinsic width is the sum of all the ruby column widths. Each ruby
column width is the maximum width of its base box and text boxes. These
individual widths are determined using GetPrefISize on the base and text boxes.
Ruby base container frames store a list of pointers to the ruby text container
frames in the segment they denote. This list of pointers is created in the ruby
frame reflow method before calling the reflow method for the ruby base
container. The list exists and is used only during reflow of the main ruby frame
and is cleared before returning from reflow.
