To reduce the complexity of the parse tree we remove the curly
element which is used for grouping in TeX. Instead, we use
use an attribute which defines if the group is put into curly
brackets or not. The functionality of the curly element
is transferred to the TexArray which was the only possible
child of the curly element before. To ease the transition,
we add a special constructor to TexArray.
We could not measure any performance implications of this change.
Bug: T333973
Change-Id: Idcb58694022831113bdc437576bb9f48658fff2f