LibGfx: Add method to Matrix that determines if the matrix is invertible

Userland/Libraries/LibGfx/Matrix.h

@@ -223,6 +223,11 @@ public:
         return result;
     }
 
+    constexpr bool is_invertible() const
+    {
+        return determinant() != 0.0;
+    }
+
 private:
     T m_elements[N][N];
 };