Support larger text-size

[asheemmamoowala]

#9208 proposed removing text-size restrictions, but then suffers from distortion in the enlarged glyphs. This could be better supported using multi-channel SDFs (gl-native discussion) or with glyphs and text being rendered entirely by the client using a local font.

[arindam1993]

We could also user larger sized sdf's, and only requesting the larger sized ones when we need them, kind of like mip levels.