Fixes #2616
First task in #3001.
Implements all missing table parameters in grid, namely align, inset, fill and stroke.
Added tests.

Implementation details

• align and inset are handled by Grid and Table themselves through the apply_align_inset_to_cells function.
• fill and stroke are handled inside GridLayouter, on .layout() (which calls .render_fills_strokes()).
• The implementations for those were just taken directly from TableElem's code.
• The way things are organized might change once table.cell and grid.cell are implemented in a future PR.

Possible improvements

• Might need to improve the doc examples (most were copied from table's docs).
• I considered moving all of Grid and Table impl Layout code to a function like layout_grid, since it's the same, but I figured that this is already more or less GridLayouter's job anyway - but I still felt like align and inset, at least for now, could be handled outside of it. So, at the moment, there is a bit of duplication, but maybe it's not that bad? I can make some layout_grid function either way if that's better.