[polly] Revise IDE folder structure

[Meinersbur]

Reviewers of #89153 suggested to break up the patch into per-subproject patches. This is the Polly part. See #89153 for the entire series and motivation.

Update the folder titles for targets in the monorepository that have not seen taken care of for some time. These are the folders that targets are organized in Visual Studio and XCode (set_property(TARGET <target> PROPERTY FOLDER "<title>")) when using the respective CMake's IDE generator.

• Ensure that every target is in a folder
• Use a folder hierarchy with each LLVM subproject as a top-level folder
• Use consistent folder names between subprojects
• When using target-creating functions from AddLLVM.cmake, automatically deduce the folder. This reduces the number of set_property/set_target_property, but are still necessary when add_custom_target, add_executable, add_library, etc. are used. A LLVM_SUBPROJECT_TITLE definition is used for that in each subproject's root CMakeLists.txt.