Slow StyleContextStack.autopush() for large table

[estanglerbm]

The styleProperties.forEach() in StyleContextStack.autopush() takes significant time for a large table of rows (i.e. 1,000 to 5,000 pages).

It's much faster (i.e. 14%) to skip creating the styleOverrideObject and just use the item itself.

This change would break three existing tests, however, that check for the number returned rather than for specific names (or lack thereof).

[liborm85]

Fixed by PR #2733.
Released in version 0.2.11.