Disable DepthTest when drawing glyphs+move shared glyph draw logic

With depth testing enabled nearby glyphs can z-fight
and so some pixels might be discarded before fragment shader
even runs, which causes us to see only part of a letter.

As such we always draw with blending enabled and depth testing
disabled so that any overlaps simply causes the char pixels to show.

res/shaders/glyph.glsl

@@ -46,7 +46,7 @@ uniform sampler2D diffTex;
 void main()
 {
     vec4 texColor = texelFetch(diffTex, ivec2(v2fUV0), 0);
-    // vec4 texColor = texture(diffTex, v2fUV0);
+    // This commented out part highlights the full region of the char
     // if (texColor.r == 0)
     // {
     //     fragColor = vec4(0,1,0,0.25);