[cuda.cooperative] Support multidimensional thread blocks in block load/store and improve load/store docs

[brycelelbach]

Description

This PR changes cuda.cooperative.block.load and cuda.cooperative.block.store to accept a multi-dimensional block shape.

Checklist

• Implementation.
• Add tests.
• Add docs.

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[brycelelbach]

@shwina @tpn @gevtushenko Please review and merge.

[bernhardmgruber]

/ok to test

[github-actions]

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👃 Inspect Changes

Modifications in project?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
	CUDA Experimental
+/-	python
	CCCL C Parallel Library
	Catch2Helper

Modifications in project or dependencies?

	Project
	CCCL Infrastructure
	libcu++
	CUB
	Thrust
	CUDA Experimental
+/-	python
	CCCL C Parallel Library
	Catch2Helper

🏃‍ Runner counts (total jobs: 1)

#	Runner
1	linux-amd64-gpu-rtx2080-latest-1