LibWeb: Add default equality operators to Available{Space,Size}

I find myself adding these over and over again while testing.
Let's just have them always there.

Userland/Libraries/LibWeb/Layout/AvailableSpace.h

@@ -47,6 +47,8 @@ public:
 
     DeprecatedString to_deprecated_string() const;
 
+    bool operator==(AvailableSize const& other) const = default;
+
 private:
     AvailableSize(Type type, CSSPixels);
 
@@ -62,6 +64,8 @@ public:
     {
     }
 
+    bool operator==(AvailableSpace const& other) const = default;
+
     AvailableSize width;
     AvailableSize height;