Sema: Allow parameterized protocol types without 'any' as the underlying type of a typealias

Just as with an unconstrained protocol type appearing here, such a typealias
can only be used on the right hand side of a conformance requirement, or as
the base of an 'any' type.

Author: slavapestov

lib/Sema/TypeCheckType.h

@@ -288,13 +288,13 @@ class TypeResolutionOptions {
     switch (context) {
     case Context::Inherited:
     case Context::ExtensionBinding:
+    case Context::TypeAliasDecl:
+    case Context::GenericTypeAliasDecl:
     case Context::GenericRequirement:
     case Context::ExistentialConstraint:
     case Context::MetatypeBase:
       return true;
     case Context::None:
-    case Context::TypeAliasDecl:
-    case Context::GenericTypeAliasDecl:
     case Context::InExpression:
     case Context::ExplicitCastExpr:
     case Context::ForEachStmt:

test/type/parameterized_protocol.swift

@@ -180,6 +180,19 @@ extension Sequence<Int> {
 }
 
 
+/// Constraint aliases
+
+typealias SequenceOfInt = Sequence<Int>
+typealias SequenceOf<T> = Sequence<T>
+
+// CHECK-LABEL: .testConstraintAlias1@
+// CHECK-NEXT: Generic signature: <T where T : Sequence, T.[Sequence]Element == Int>
+func testConstraintAlias1<T : SequenceOfInt>(_: T) {}
+
+// CHECK-LABEL: .testConstraintAlias2@
+// CHECK-NEXT: Generic signature: <T where T : Sequence, T.[Sequence]Element == String>
+func testConstraintAlias2<T : SequenceOf<String>>(_: T) {}
+
 /// Protocol compositions
 
 // CHECK-LABEL: .testComposition1@