Added glsl 100 and 120 shaders to lightmap example. (#3543)

* Added glsl 100 and 120 shaders to lightmap example.

* Fixed lightmap example resource loading on web.

examples/shaders/resources/shaders/glsl120/lightmap.fs

@@ -0,0 +1,20 @@
+#version 120
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec2 fragTexCoord2;
+varying vec3 fragPosition;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform sampler2D texture1;
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture2D(texture0, fragTexCoord);
+    vec4 texelColor2 = texture2D(texture1, fragTexCoord2);
+
+    gl_FragColor = texelColor * texelColor2;
+}