SIL: Record whether vtable entries are inherited or overridden

Consider a class hierarchy like the following:

class Base {
  func m1() {}
  func m2() {}
}

class Derived : Base {
  override func m2() {}
  func m3() {}
}

The SIL vtable for 'Derived' now records that the entry for m1
is inherited, the entry for m2 is an override, and the entry
for m3 is a new entry:

sil_vtable Derived {
  #Base.m1!1: (Base) -> () -> () : _T01a4BaseC2m1yyF [inherited]
  #Base.m2!1: (Base) -> () -> () : _T01a7DerivedC2m2yyF [override]
  #Derived.m3!1: (Derived) -> () -> () : _T01a7DerivedC2m3yyF
}

This additional information will allow IRGen to emit the vtable
for Derived resiliently, without referencing the symbol for
the inherited method m1() directly.

include/swift/Serialization/ModuleFormat.h

@@ -54,7 +54,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
-const uint16_t VERSION_MINOR = 355; // Last change: extension dependencies
+const uint16_t VERSION_MINOR = 356; // Last change: SILVTable::Entry::Kind
 
 using DeclID = PointerEmbeddedInt<unsigned, 31>;
 using DeclIDField = BCFixed<31>;