Span: Add missing move constructors

modules/juce_core/containers/juce_Span.h

@@ -114,6 +114,10 @@ public:
 
     constexpr Span& operator= (const Span&) = default;
 
+    constexpr Span (Span&&) noexcept = default;
+
+    constexpr Span& operator= (Span&&) noexcept = default;
+
     using Base::size;
 
     constexpr Value* begin() const { return ptr; }