Improve handling of extremely large glyphs

[QuantumBadger]

Currently, huge glyphs larger than 1024x1024px will not be rendered, as that is the current size of each texture in the glyph cache.

It would be good to handle this better, perhaps by:

• Dynamically increasing the cache texture size, after detecting GPU support
• Bypassing the cache entirely to avoid high memory usage (would likely incur poor performance)

[QuantumBadger]

Another way this would be possible is to split up huge glyphs into multiple texture cache entries, e.g. to split a 4096x4096 glyph into 16 squares of 1024x1024.