Deserialize annotations on class members

Make 'Callable' message of descriptors.proto extensible, extend it in
java_descriptors.proto with a JVM signature of the member. This is needed in
order for annotation deserializer to find out which member in the compiled
bytecode corresponds to which descriptor in the hierarchy.

Create a new module 'serialization.java' containing everything related to
Java-specific serialization of descriptors.

Add an extension point to DescriptorSerializer, allowing to perform
platform-specific serialization on a callable

compiler/testData/loadKotlin/annotations/classMembers/Function.txt

@@ -0,0 +1,10 @@
+package test
+
+internal final annotation class Anno : jet.Annotation {
+    /*primary*/ public constructor Anno()
+}
+
+internal final class Class {
+    /*primary*/ public constructor Class()
+    test.Anno() internal final fun foo(): jet.Unit
+}