- IR plugin does not use it anymore,
regular annotation instantiation feature is used
(insertion of IrConstructorCall(annotationCtorSymbol)).
- IR plugin still generates `SerialInfo$Impl` class to be compatible
with previously compiled code & libraries.
- Custom implementation over descriptors in IR plugin is removed;
plugin now delegates to the existing lowering with some tweaks.
- $Impl descriptor is removed from FE 1.0 because it is no longer needed
for IR plugin; it shouldn't be exposed to users so FIR doesn't need it either.
- Since language lowering is now used, it is possible to correctly instantiate
SerialInfo annotations with default values even if they are from other modules
and even if they were not processed by the plugin.
#KT-48733 Fixed
Fixes https://github.com/Kotlin/kotlinx.serialization/issues/1574
Leonid Startsev
f1b1837f40