Implement Label3D node.

Add "generate_mipmap" font import option.
Add some missing features to the Sprite3D.
Move BiDi override code from Control to TextServer.
Add functions to access TextServer font cache textures.
Add MSDF related flags and shader to the standard material.
Change standard material cache to use HashMap instead of Vector.

drivers/gles3/shaders/canvas.glsl

@@ -478,10 +478,6 @@ float msdf_median(float r, float g, float b, float a) {
 	return min(max(min(r, g), min(max(r, g), b)), a);
 }
 
-vec2 msdf_map(vec2 value, vec2 in_min, vec2 in_max, vec2 out_min, vec2 out_max) {
-	return out_min + (out_max - out_min) * (value - in_min) / (in_max - in_min);
-}
-
 void main() {
 	vec4 color = color_interp;
 	vec2 uv = uv_interp;