Handle Vector4 default input values in visual shaders
When set_input_port_default_value in a VisualShaderNodeCustom is called with a Vector4 as the second parameter and nothing is connected to the input, shader code generator inserts empty space instead of the default value.
This PR should fix this by making code generator handle 4d vectors the same way as 3d and 2d.
~~I don't yet have an environment set up to properly build and test this, so the changes may be not valid.~~
UPD: Tested the build from github actions. Seems to work fine.
cc @Chaosus Please take a look.
@arkology the relevant teams have been requested, please have some patience
Thanks! And congrats for your first merged Godot contribution :tada: