Make draw data creation no longer require a mutable re_renderer context

[Wumpf]

What

• Prerequisite for Parallelize space views #1325
• Follow-up of Interior mutablilty for re_renderer's static resource pools (RenderPipeline/Shader/Layouts/etc.) #4421
• Followed by Make viewer contexts's render context reference non-mutable #4430

Make draw data (this is in essence resource submission to GPU! e.g. make pointcloud ready to render) an operation that doesn't require a mutable renderer context.

Two pieces to this:

• FileResolver resolve needs to be non-mut, this turned out to be trivial
• Renderer::get_or_create had to be streamlined. Renderer creation is now done directly on the context and holding a renderer implies holding a read lock. Since Renderers are added very rarely, this isn't much of a limitation!

This causes a large trickle of removing &mut and gets us almost to having a non-mutable render context reference on the Viewer context!

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
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• I have tested the web demo (if applicable):
  • Full build: app.rerun.io
  • Partial build: [app.rerun.io](https://app.rerun.io/pr/4422/index.html?manifest_url=https://app.rerun.io/version
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

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Part of series towards more multithreading in the viewer!

• Selection state is now fully double buffered and has interior mutability #4387
• Enable (selected) new cargo clippy lints #4404
• Time control is now behind a RwLock, making recording config access non-mutable everywhere #4389
• Interior mutablilty for re_renderer's static resource pools (RenderPipeline/Shader/Layouts/etc.) #4421
• You are here ➡️ Make draw data creation no longer require a mutable re_renderer context  #4422
• Make viewer contexts's render context reference non-mutable #4430

[emilk]

We shouldn't need unwrap. get_or_create should just return the gotten or created thing

Suggested change

	{
	self.renderers.write().get_or_create::<_, R>(
	&self.shared_renderer_data,
	&self.gpu_resources,
	&self.device,
	&self.resolver,
	);
	}
	// Release write lock again and only take a read lock.
	// safe to unwrap since we just created it.
	parking_lot::RwLockReadGuard::map(self.renderers.read(), |r| r.get::<R>().unwrap())
	self.renderers.write().get_or_create::<_, R>(
	&self.shared_renderer_data,
	&self.gpu_resources,
	&self.device,
	&self.resolver,
	)

[Wumpf]

the problem with that is that we have to release the write lock first! The result of get_or_create implies keeping the write lock and we don't want to do that.