Missing files in Visual Studio solutiun/projects when generated from Cmake

If you generate a Visual Studio project using a command like cmake --preset=test-msvc and then open the generated solution in Visual Studio a number of files are missing. This is mostly header files which is reasonable as most build systems like ninja or make don't need to "see" the header files and a #include will find them fine. However if you want to edit them in an IDE it's a pain no having them.

So the PR I will submit does the following

1. Files like src/ifc-dom/common.hxx are added to the relevant project
2. Adds the following custom target. This is a target that does nothing in the build. It does however show up in the IDE

add_custom_target(ifc-include SOURCES
    include/ifc/abstract-sgraph.hxx
    include/ifc/assertions.hxx
    include/ifc/basic-types.hxx
    include/ifc/file.hxx
    include/ifc/index-utils.hxx
    include/ifc/operators.hxx
    include/ifc/pathname.hxx
    include/ifc/pp-forms.hxx
    include/ifc/reader.hxx
    include/ifc/source-word.hxx
    include/ifc/tooling.hxx
    include/ifc/underlying.hxx
    include/ifc/util.hxx
    include/ifc/version.hxx
    include/ifc/dom/node.hxx
)

3. Add the following VS_SOLUTION_ITEMS property. This makes the files show up as solution files in the VS IDE. VS_SOLUTION_ITEMS is a new cmake 4.0 feature. If you use an older cmake or generate for ninja or similar the VS_SOLUTION_ITEMS property is just ignored.

set( SolutionItems
    .clang-format
    .gitignore
    CMakePresets.json
    LICENSE.txt
    README.md
    vcpkg.json)
set_property(DIRECTORY APPEND PROPERTY VS_SOLUTION_ITEMS ${SolutionItems})
source_group("Solution Items" FILES ${SolutionItems})

4. Stop the files in a project being put into sub folders with names like "Sources" and "Headers". This may be useful if you have a lot of file in a project but is extremely annoying if you don't. I don't think this would have an effect on other generators but there is a guard just in case

# By default we don't want the Visual Studio default "sources" and "headers" folders, the following put's everything directly in the project. 
if (${CMAKE_GENERATOR} MATCHES "^Visual Studio")
    source_group( " "  REGULAR_EXPRESSION .*)
endif()

Start by running cmake --preset=test-msvc and opening the generated solution in Visual Studio to reproduce the missing files and folder layout. Review the CMake configuration that defines the relevant projects, including the ifc-include target and VS_SOLUTION_ITEMS example in the issue. Done means the listed headers and solution items appear in Visual Studio, without unwanted Sources or Headers folders, while other generators remain unaffected.