[css-align-3] mixing baseline self-alignment and content alignment

[fantasai]

If both baseline content-alignment and baseline self-alignment are specified in the same axis on the same box, only baseline self-alignment is honored in that axis; the content-alignment in that axis must be treated as start.

Two problems with this text:

1. It doesn't specify how non-baseline values of content-alignment interact with baseline self-alignment. Blink does content-alignment first, and then baseline self-aligns (which is good behavior) whereas Firefox does baseline self-alignment first and then content aligns (which results in something that looks totally random).
2. For last baseline-alignment, we probably want to treat it as end rather than start.