Effects: add (de)serialization of contracts in metadata

- Introduce new definitions in descriptors.proto
- Add new corresponding values in Flags.java
- Introduce ContractSerializer and ContractDeserializer, responsible for
for conversion ContractDescription <-> ProtoBuf.Contract
- Add dependency of 'serialization' module on 'resolution' so that it
could see contracts model.

Note that here we do a lot of seemingly unnecessary hoops, which in fact
necessary to respect existing module system (in particular, to be able
to extract ContractDescription declarations from 'descriptors' module to
make them invisible from reflection)

==========
Effect System introduction: 8/18

compiler/resolution/src/org/jetbrains/kotlin/contracts/description/LazyContractProvider.kt

@@ -17,12 +17,13 @@
 package org.jetbrains.kotlin.contracts.description
 
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.serialization.deserialization.ContractProvider
 
 /**
  * Essentially, this is a composition of two fields: value of type 'ContractDescription' and
  * 'computation', which guarantees to initialize this field.
  */
-class LazyContractProvider(private val computation: () -> Any?) {
+class LazyContractProvider(private val computation: () -> Any?) : ContractProvider {
     @Volatile
     private var isComputed: Boolean = false