build: replace FetchContent with direct includes for glm

include/glm/ext/matrix_float2x3.hpp

@@ -0,0 +1,18 @@
+/// @ref core
+/// @file glm/ext/matrix_float2x3.hpp
+
+#pragma once
+#include "../detail/type_mat2x3.hpp"
+
+namespace glm
+{
+	/// @addtogroup core_matrix
+	/// @{
+
+	/// 2 columns of 3 components matrix of single-precision floating-point numbers.
+	///
+	/// @see <a href="http://www.opengl.org/registry/doc/GLSLangSpec.4.20.8.pdf">GLSL 4.20.8 specification, section 4.1.6 Matrices</a>
+	typedef mat<2, 3, float, defaultp>		mat2x3;
+
+	/// @}
+}//namespace glm