Remove utility method from AnnotationDescriptor interface
Rename NameTable -> StringTable in serialization

Since almost the beginning, it was also used to store arbitrary strings, not
just names
Minor, remove unnecessary NOTHING_TO_INLINE suppressions
Introduce extension for built-ins serialization, drop .kotlin_class_names
Introduce binary representation for annotations

Will be used where annotations can't be stored elsewhere: for example,
built-ins, JS, type annotations on JDK<8
Add ProtoBufConsistencyTest

This test checks that indices of all extensions on the same message type are
unique across different extension points (JVM, built-ins, ...)