Document font_size

[rparrett]

How can Bevy's documentation be improved?

The font_size field of TextStyle can be confusing.

It corresponds to the vertical height of glyphs in pixels on the font atlas texture when they are rasterized. In other words, it is the text "resolution."

Additionally (I think) it is multiplied by the window scale factor, but not by camera scale.

With default camera/ui scaling, this is 1:1 with screen pixels, so it is often treated as a "text size." But this can be surprising to users with custom scaling, and we should at least mention this in the docs.

With a Text2dBundle and a zoomed-in camera, text will appear large and pixelated. With a zoomed-out camera, text will appear small.

With a TextBundle and a UI camera and higher UI scales, text will be larger (but not pixelated, I think?), etc.

Whoever picks this up should verify these statements.