Draft: Add a view to raw vector data with `DenseVector` interface

Summary

This MR introduces a span DenseVectorSpan over a consecutive sequence of values with a given number. This span has an interface like a DenseVector and can be used in all the places where a DenseVector is expected, e.g. in DenseMatrix::solve. This allows to wrap non-Dune types like std::vector in the Dune interface. It also would allow to replace the ScalarVectorView since a single scalar value is just a sequence of length 1.

Requirements

• This MR is based on !1334 (merged)

Note

A similar span can be easily introduced for matrices. A generalization is already implemented for "tensors" in https://gitlab.dune-project.org/simon.praetorius/dune-tensor/-/blob/main/dune/tensor/tensorspan.hh?ref_type=heads

changed target branch from feature/mdspan to master

mentioned in issue #4

changed the description

changed milestone to %DUNE 2.11.0

mentioned in merge request dune-localfunctions!264 (merged)

marked the checklist item This MR is based on !1334 (merged) as completed

added 275 commits

• d5d5d842...590466b3 - 271 commits from branch master
• 9ee6320d - Make layout mapping modifyable
• 5b0e47e7 - Add the extract_container() member to mdarray
• dca9e07b - Add a view to raw vector data with DenseVector interface
• 66faab72 - Base the implementation on mdspan

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mentioned in merge request staging/dune-functions!499

added 9 commits

• 66faab72...b6c3557f - 4 commits from branch master
• c5e1ec62 - Make layout mapping modifyable
• 8116d652 - Add the extract_container() member to mdarray
• 06c67e05 - Add a view to raw vector data with DenseVector interface
• 9eb966b4 - Base the implementation on mdspan
• fe2d7d15 - Cleanup the constructors and extend the deduction guides

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added 1 commit

• 2168e579 - Add include for concept checks

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added 26 commits

• 2168e579...0298f0f7 - 20 commits from branch master
• 910eb8ee - Make layout mapping modifyable
• 245a99f3 - Add the extract_container() member to mdarray
• 855464af - Add a view to raw vector data with DenseVector interface
• 1180f3ef - Base the implementation on mdspan
• 094c1aab - Cleanup the constructors and extend the deduction guides
• ad73ffaa - Add include for concept checks

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added 1 commit

• 1424ecfe - Add test for DenseVectorSpan

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added 1 commit

• 3717983a - Extend the DenseVectorSpan test and deduction guides

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mentioned in issue staging/dune-functions#89 (closed)

mentioned in issue dune-fem/dune-fem#237 (closed)

mentioned in merge request !1433