Fix origin being included in per viewport grid visibility toggle, and add ability to hide it seperately

[ryevdokimov]

#88584 added the ability to hide the grid per viewport, but accidentally included the origin, which is technically a bug. This PR separates them out, and now both can be toggled.

2025-02-08.12-52-18.mp4

[aaronfranke]

When the origin is not drawn, the grid lines are supposed to be drawn in its place.

[ryevdokimov]

When the origin is not drawn, the grid lines are supposed to be drawn in its place.

Good catch, I modified the code so that the origin lines have a higher render priority so that they are always on top of the grid lines and removed the need to have to rebuild the grid.

[badsectoracula]

The PR seems to work as expected, but IMO this is more of a new feature than a bug fix - since essentially it adds the option to toggle the grid and origin separately, adding to the UI of an already overloaded menu - so i think it is a good idea to make a feature suggestion for this and link this PR from it.

[ryevdokimov]

There is a proposal linked above that effectively covers that godotengine/godot-proposals#11363. I agree as well that the menu is overloaded, but I do believe there is another proposal to clean that up.

Edit: Found it: godotengine/godot-proposals#11256