shader: replace texture2d with texture (#10893)

* shader: replace texture2d with texture

remove unused v_color and replace deprecated texture2d with texture.

* shader: use the more modern essl3 extension

GL_OES_EGL_image_external_essl3 provides support for samplerExternalOES
in texture function, aquamarine already use it. apply it here too.

src/render/shaders/glsl/rgba.frag

@@ -18,7 +18,7 @@ uniform vec3 tint;
 layout(location = 0) out vec4 fragColor;
 void main() {
 
-    vec4 pixColor = texture2D(tex, v_texcoord);
+    vec4 pixColor = texture(tex, v_texcoord);
 
     if (discardOpaque == 1 && pixColor[3] * alpha == 1.0)
 	    discard;