LibGfx/JBIG2: Add two more tests for context reuse in symbol bitmaps

Currently, if I'm not mistaken there exists a single test case `bitmap-symbol-context-reuse` for this, where `refagg=0` and `huffman=0`. I think it would be nice to have another test with `refagg=1` and `huffman=0`, as well as `refagg=1` and `huffman=1`.