It affects the `is IrGetField` check in
TypeOperatorLowering.computeNotNullAssertionText, which leads to missing
NPE messages when accessing backing fields of public properties.
#KT-64615
Disabling of this language feature (see KT-57570) was not supported in
the (default) light tree mode, and after this change it will not be
supported in the PSI mode as well. This makes the behavior more
consistent and allows us to remove the directive
IGNORE_BACKEND_K2_LIGHT_TREE in the future (KT-56757).
Alexander Udalov