Files listed in the `VS_SOLUTION_ITEMS` directory property of a project
directory are added as solution items in the 'Solution Items' solution
directory.
If `source_group` is applied to the files listed in `VS_SOLUTION_ITEMS`,
solution groups matching the names of the source groups are created
outside of the default 'Solution Items' group. If not items are placed
into the default group, it is not created.
Solution items added to subprojects are not included in the top-level
project.
Closes: #26409
0bb13ba0e6