[ABI] Renamed method descriptor's SignedAsData to IsAsync.

In 26b3549, new bits were spoken for in
MethodDescriptorFlags and ProtocolRequirementFlags to indicate that a
field is an async function pointer and as such must is treated as data
for the purposes of ptrauth.

Previously, that bit was named IsSignedAsData because indeed async
function pointers must be signed and authed as data.

We should make the representation semantic, however, so here that name
is changed to IsAsync.

Author: nate-chandler

include/swift/ABI/MetadataValues.h

@@ -317,7 +317,7 @@ class MethodDescriptorFlags {
     KindMask = 0x0F,                // 16 kinds should be enough for anybody
     IsInstanceMask = 0x10,
     IsDynamicMask = 0x20,
-    IsSignedAsDataMask = 0x40,
+    IsAsyncMask = 0x40,
     ExtraDiscriminatorShift = 16,
     ExtraDiscriminatorMask = 0xFFFF0000,
   };
@@ -346,12 +346,12 @@ class MethodDescriptorFlags {
     return copy;
   }
 
-  MethodDescriptorFlags withIsSignedAsData(bool isSignedAsData) const {
+  MethodDescriptorFlags withIsAsync(bool isAsync) const {
     auto copy = *this;
-    if (isSignedAsData)
-      copy.Value |= IsSignedAsDataMask;
+    if (isAsync)
+      copy.Value |= IsAsyncMask;
     else
-      copy.Value &= ~IsSignedAsDataMask;
+      copy.Value &= ~IsAsyncMask;
     return copy;
   }
 
@@ -372,7 +372,7 @@ class MethodDescriptorFlags {
   /// Note that 'init' is not considered an instance member.
   bool isInstance() const { return Value & IsInstanceMask; }
 
-  bool isSignedAsData() const { return Value & IsSignedAsDataMask; }
+  bool isAsync() const { return Value & IsAsyncMask; }
 
   uint16_t getExtraDiscriminator() const {
     return (Value >> ExtraDiscriminatorShift);
@@ -539,7 +539,7 @@ class ProtocolRequirementFlags {
   enum : int_type {
     KindMask = 0x0F,                // 16 kinds should be enough for anybody
     IsInstanceMask = 0x10,
-    IsSignedAsDataMask = 0x20,
+    IsAsyncMask = 0x20,
     ExtraDiscriminatorShift = 16,
     ExtraDiscriminatorMask = 0xFFFF0000,
   };
@@ -559,12 +559,12 @@ class ProtocolRequirementFlags {
     return copy;
   }
 
-  ProtocolRequirementFlags withIsSignedAsData(bool isSignedAsData) const {
+  ProtocolRequirementFlags withIsAsync(bool isAsync) const {
     auto copy = *this;
-    if (isSignedAsData)
-      copy.Value |= IsSignedAsDataMask;
+    if (isAsync)
+      copy.Value |= IsAsyncMask;
     else
-      copy.Value &= ~IsSignedAsDataMask;
+      copy.Value &= ~IsAsyncMask;
     return copy;
   }
 
@@ -582,7 +582,7 @@ class ProtocolRequirementFlags {
   /// Note that 'init' is not considered an instance member.
   bool isInstance() const { return Value & IsInstanceMask; }
 
-  bool isSignedAsData() const { return Value & IsSignedAsDataMask; }
+  bool isAsync() const { return Value & IsAsyncMask; }
 
   bool isSignedWithAddress() const {
     return getKind() != Kind::BaseProtocol;