LibGfx: Mark some `Matrix` functions as `[[nodiscard]]`

Userland/Libraries/LibGfx/Matrix.h

@@ -92,7 +92,7 @@ public:
         return division;
     }
 
-    constexpr Matrix adjugate() const
+    [[nodiscard]] constexpr Matrix adjugate() const
     {
         if constexpr (N == 1)
             return Matrix(1);
@@ -107,7 +107,7 @@ public:
         return adjugate;
     }
 
-    constexpr T determinant() const
+    [[nodiscard]] constexpr T determinant() const
     {
         if constexpr (N == 1) {
             return m_elements[0][0];
@@ -122,7 +122,7 @@ public:
         }
     }
 
-    constexpr T first_minor(size_t skip_row, size_t skip_column) const
+    [[nodiscard]] constexpr T first_minor(size_t skip_row, size_t skip_column) const
     {
         static_assert(N > 1);
         VERIFY(skip_row < N);
@@ -145,7 +145,7 @@ public:
         return first_minor.determinant();
     }
 
-    constexpr static Matrix identity()
+    [[nodiscard]] constexpr static Matrix identity()
     {
         Matrix result;
         for (size_t i = 0; i < N; ++i) {
@@ -159,14 +159,14 @@ public:
         return result;
     }
 
-    constexpr Matrix inverse() const
+    [[nodiscard]] constexpr Matrix inverse() const
     {
         auto det = determinant();
         VERIFY(det != 0);
         return adjugate() / det;
     }
 
-    constexpr Matrix transpose() const
+    [[nodiscard]] constexpr Matrix transpose() const
     {
         Matrix result;
         for (size_t i = 0; i < N; ++i) {