Ensure text rendering is always sharp

Defaulting to larger font size, while adequate as quick fix, doesn't solve the underlying issue of blurry text. Proper fix needs adjusting the font pixelsize according to the selected pixelsize and maximum scaling the text element has during the animation.

This will always produce sharp fonts (once we have distance field font rendering in place).

When implementing this, investigate if glyps are actually re-rasterized when using distance field rendering or not as the distance field should scale quite well. If re-rasterizing doesn't occur then it's ok to change the font size on the fly during animitions. If re-rasterization occurs we should lock the pixelsize for the entire animation.