Remove screen size dependency

[hecrj]

Fixes #63.

This removes the screen size dependency as I described in #63. These are just the basic changes to get the gfx_glyph paragraph example to work. All the other examples probably need to be adapted.

I personally think the code becomes much simpler. Let me know what you think and how to proceed.

[alexheretic]

Thanks I think this looks promising. I made a version without the invert-y stuff to see if it would work and it seems fine. I also adapted the opengl example.

The pre_positioned example is now broken for resizing, previously the screen dimension change would trigger a vertex re-calc, but I'm not sure why this is needed now...

[alexheretic]

Ok cool I figured out why pre_positioned broke. gfx render target is mostly internally Arcs except the dimension, so when you clone it and update the original dimensions it won't update the clones.

So in this example the pipe render target had wrong dimensions after resizing.

[alexheretic]

Ok this looks good to me. Can you check I haven't screwed up your changes too much?

I'll test this with my usages and double check everything is fine.

[alexheretic]

Thanks @hecrj! This is a nice improvement.

[hecrj]

Looks good to me! I have integrated the changes with wgpu_glyph locally and it's all working well.

Thank you for your fast response!