Refactoring for lang.test
More refactoring and new constraints testing functionality
MPS-19364 Added intention for rule specification in test
Fixes in constraints to accept null in IOperationContext
Constraints refactoring: removing IOperationContext, resolving TODOs of Timur
Merge branch 'master' into 3.1/fix_tests_tag_for_constraints
Generation fix
Merge branch 'master' into 3.1/fix_tests_tag_for_constraints