Migrate OpenGL string-literals to embedded files

Rather than declaring a big C++ literal for these strings, they are now
proper `.vert` and `.frag` files that will become embedded into the
application at build-time. It also allows for clang-format to format the
glsl files the same as our C++ code. CMake will also automatically track
and re-embed the file if it detects that the glsl source files have
changed since the last build. Ex, making a change to
`opengl_display.frag` and compiling will automatically recompile and
link the resource-target that it is associated with.

src/host_shaders/opengl_display.vert

@@ -0,0 +1,23 @@
+#version 410 core
+out vec2 UV;
+
+void main() {
+	const vec4 positions[4] = vec4[](
+		vec4(-1.0, 1.0, 1.0, 1.0),   // Top-left
+		vec4(1.0, 1.0, 1.0, 1.0),    // Top-right
+		vec4(-1.0, -1.0, 1.0, 1.0),  // Bottom-left
+		vec4(1.0, -1.0, 1.0, 1.0)    // Bottom-right
+	);
+
+	// The 3DS displays both screens' framebuffer rotated 90 deg counter clockwise
+	// So we adjust our texcoords accordingly
+	const vec2 texcoords[4] = vec2[](
+		vec2(1.0, 1.0),  // Top-right
+		vec2(1.0, 0.0),  // Bottom-right
+		vec2(0.0, 1.0),  // Top-left
+		vec2(0.0, 0.0)   // Bottom-left
+	);
+
+	gl_Position = positions[gl_VertexID];
+	UV = texcoords[gl_VertexID];
+}