Add support for writing-mode="rl-tb" (right-to-left) in FO outputs.

Add support for writing-mode="rl-tb" (right-to-left) in FO outputs.
Changed instances of margin-left to margin-{$direction.align.start}
and margin-right to margin-{$direction.align.end}. Those direction.align
params are computed from the writing mode value in each locale's
gentext key named 'writing-mode', introduced in 1.74.3 to add
right-to-left support to HTML outputs.