[Sema] Non-requirement protocol members should inherit @usableFromInline

Previously, members of protocols that were not protocol requirements,
like accessors and typealiases, did not inherit @usableFromInline from
the parent protocol. Change this so they do.

Author: Harlan Haskins

lib/AST/Decl.cpp

@@ -2411,8 +2411,7 @@ bool ValueDecl::isUsableFromInline() const {
       return true;
 
   if (auto *containingProto = dyn_cast<ProtocolDecl>(getDeclContext())) {
-    if (isProtocolRequirement() &&
-        containingProto->getAttrs().hasAttribute<UsableFromInlineAttr>())
+    if (containingProto->getAttrs().hasAttribute<UsableFromInlineAttr>())
       return true;
   }
 

test/Compatibility/attr_inlinable_swift42.swift

@@ -17,3 +17,12 @@ enum InternalEnum {
   case persimmon(String)
 }
 
+@usableFromInline protocol P {
+  typealias T = Int
+}
+
+extension P {
+  @inlinable func f() {
+    _ = T.self // typealiases were not checked in Swift 4.2, but P.T inherits @usableFromInline in Swift 4.2 mode
+  }
+}

test/attr/attr_inlinable.swift

@@ -248,3 +248,13 @@ public struct KeypathStruct {
     // expected-error@-1 {{property 'x' is internal and cannot be referenced from an '@inlinable' function}}
   }
 }
+@usableFromInline protocol P {
+  typealias T = Int
+}
+
+extension P {
+  @inlinable func f() {
+    _ = T.self // ok, typealias inherits @usableFromInline from P
+  }
+}
+