In idea plugin: clean-up of PSI to virtual file relation.
MPSTreeStructureProvider clean up: hiding files that constitute data source for a FolderDataSource from idea project pane. I.e. not showing .mpsr files
FolderDataSource has a method changed from protected to public
MPSPsiModel: being careful to to return null as mySourceVirtualFile
MPSPsiModel: use VirtualFIleUtils instead of LocalFileSystem directly
Model replace event now also leads to psi update (for psi built over our models). Model replace typicaly happens in reload session.
FolderDataSource: add/remove file now increase dataSource.getTimestamp(). In case if (for example) file-per-root model, adding/removing root node file now leads to model reload
null-safety in MPSPsiClassifier.hasModifierProperty()