GLES2 polyline drawn as GL_LINE_STRIP to match GLES3
GLES2 polyline drawn as GL_LINE_STRIP to match GLES3

The behaviour of TYPE_POLYLINE appeared incorrect in GLES2, and inconsistent with GLES3 and the docs, which state that draw_polyline 'Draws interconnected line segments'. Also when drawing with triangles GLES2 draws interconnected segments.

This PR simply changes the primitive from GL_LINES to GL_LINE_STRIP as in GLES3.

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot