Make protocol methods generic over <Self>.

Pull the implicit 'Self' associated type out of the protocol and into
an implicitly-declared generic parameter list for the protocol. This
makes all of the methods of a protocol polymorphic, e.g., given

  protocol P {
    typealias Assoc
    func getAssoc() -> Assoc
  }

the type of P.getAssoc is:

  <Self : P> (self : @inout P) -> () -> Self.Assoc

This directly expresses the notion that protocol methods are
polymorphic, even though 'Self' is always implicitly bound. It can be
used to simplify IRgen and some parts of the type checker, as well as
laying more of the groundwork for default definitions within
protocols as well as sundry other improvements to the generics
system.

There are a number of moving parts that needed to be updated in tandem
for this. In no particular order:
  - Protocols always get an implicit generic parameter list, with a
  single generic parameter 'Self' that conforms to the protocol itself.
  - The 'Self' archetype type now knows which protocol it is
  associated with (since we can no longer point it at the Self
  associated type declaration).
  - Protocol methods now get interface types (i.e., canonicalizable
  dependent function types).
  - The "all archetypes" list for a polymorphic function type does not
  include the Self archetype nor its nested types, because they are
  handled implicitly. This avoids the need to rework IRGen's handling
  of archetypes for now.
  - When (de-)serializing a XREF for a function type that has an
  interface type, use the canonicalized interface type, which can be
  meaningfully compared during deserialization (unlike the
  PolymorphicFunctionType we'd otherwise be dealing with).
  - Added a SIL-specific type attribute @sil_self, which extracts the
  'Self' archetype of a protocol, because we can no longer refer to
  the associated type "P.Self". 




Swift SVN r9066

lib/Serialization/ModuleFormat.h

@@ -402,7 +402,7 @@ namespace decls_block {
     IdentifierIDField,   // name
     BCFixed<1>,          // primary?
     TypeIDField,         // index if primary, parent if non-primary
-    DeclIDField,         // associated type decl
+    DeclIDField,         // associated type or protocol decl
     TypeIDField,         // superclass
     BCArray<DeclIDField> // conformances
     // Trailed by the nested types record.
@@ -506,6 +506,7 @@ namespace decls_block {
     GENERIC_TYPE_PARAM_DECL,
     IdentifierIDField, // name
     DeclIDField, // context decl
+    BCFixed<1>,  // implicit flag
     BCVBR<4>,    // depth
     BCVBR<4>,    // index
     TypeIDField, // superclass type
@@ -564,6 +565,7 @@ namespace decls_block {
     BCFixed<1>,  // class protocol?
     BCFixed<1>,  // objc?
     BCArray<DeclIDField> // protocols
+  // Trailed by the generic parameters (if any) and the decl context record
   >;
 
   using ConstructorLayout = BCRecordLayout<