[NFC] Expose default param specifier computation

Make this logic accessible outside of the mangler.

Author: beccadax

include/swift/AST/Types.h

@@ -2377,6 +2377,10 @@ enum class ParamSpecifier : uint8_t {
 
 StringRef getNameForParamSpecifier(ParamSpecifier name);
 
+/// What does \c ParamSpecifier::Default mean for a parameter that's directly
+/// attached to \p VD ? Pass \c nullptr for the value for a closure.
+ParamSpecifier getDefaultParamSpecifier(const ValueDecl *VD);
+
 /// Provide parameter type relevant flags, i.e. variadic, autoclosure, and
 /// escaping.
 class ParameterTypeFlags {

lib/AST/ASTMangler.cpp

@@ -3302,8 +3302,7 @@ void ASTMangler::appendFunctionSignature(AnyFunctionType *fn,
   }
 }
 
-static ParamSpecifier
-getDefaultOwnership(const ValueDecl *forDecl) {
+ParamSpecifier swift::getDefaultParamSpecifier(const ValueDecl *forDecl) {
   // `consuming` is the default ownership for initializers and setters.
   // Everything else defaults to borrowing.
   if (!forDecl) {
@@ -3374,7 +3373,7 @@ getParameterFlagsForMangling(ParameterTypeFlags flags,
 void ASTMangler::appendFunctionInputType(
     AnyFunctionType *fnType, ArrayRef<AnyFunctionType::Param> params,
     GenericSignature sig, const ValueDecl *forDecl, bool isRecursedInto) {
-  auto defaultSpecifier = getDefaultOwnership(forDecl);
+  auto defaultSpecifier = getDefaultParamSpecifier(forDecl);
 
   switch (params.size()) {
   case 0: