Introduce text_size_info and change back where text is positioned

[vbfox]

text_size_info can give both the box where the font wants to be logically placed to form a line (But depending on the font it might draw pixels out of this box) and the pixel-bounding box where pixels were really placed.

I know that it'll be controversial as it changes some details from #689 but I think it's the right choice:

• Fonts can put pixels out of any of the "logical" bounds passed to them, most of the time it's a little overshoot but some fonts can draw widely out of their boxes. px_bounds doc essentially says "everything goes" and trying to guess the pixel size from the reported logical size by the font is bound to create errors.
• Sometimes when positioning you want the logical box (To position more text after/under) and sometimes the pixels (To visually center the pixels)

By providing both, the consumer can take correct decisions.

I'm not sure what text_size should return, as the logical size is bound to be a bit surprising (some pixels would go out of there) but the pixel size is useless to position text relative to other text...

I'm opening this PR more as a discussion starter, as I think whatever design ends up being the final one the coordinate system and it's relation with the sizing methods need to be documented in the draw methods.