Extend mdspan interface and fix mdspan memory layout mapping

docs/source/api/composer.rst

docs/source/api/lang.rst

docs/source/conf.py

src/pystencilssfg/composer/basic_composer.py

src/pystencilssfg/emission/clang_format.py

src/pystencilssfg/lang/cpp/std_mdspan.py

src/pystencilssfg/lang/expressions.py

tests/generator_scripts/index.yaml

tests/generator_scripts/source/JacobiMdspan.harness.cpp

tests/generator_scripts/source/JacobiMdspan.py

tests/generator_scripts/source/MdSpanFixedShape.harness.cpp

tests/generator_scripts/source/MdSpanFixedShapeLayouts.py

tests/generator_scripts/source/MdSpanLbStreaming.harness.cpp

tests/generator_scripts/source/MdSpanLbStreaming.py