CanvasItem::draw_polyline Support thin polylines drawn using line strip

[kleonc]

Follow-up to #69851 aiming to solve the remaining parts:

• CanvasItem.draw_polyline ❌ - The thin option is not supported.
• CanvasItem.draw_polyline_colors ❌ - The thin option is not supported.
• CanvasItem.draw_arc ❌ - The thin option is not supported.
• RenderingServer.canvas_item_add_polyline ❌ - The thin option is not supported.

This PR makes the width parameter for the methods listed above work consistently with the other methods changed in #69851 i.e. width < 0 results in drawing thin polyline using line strip (arc is drawn as polyline too). For width >= 0 a scalable polyline is drawn using triangle strips, this is unchanged.

In the changed methods I've made antialiasing not supported for width < 0. In some methods unchanged by this PR e.g. in CanvasItem::draw_line antialiasing for width < 0 is "supported" but it's done in the same manner as for the width >= 0 case. This results in a buggy behavior because at different zoom levels the line itself remains thin but the triangle strips used for antialiasing do scale. Hence I haven't added similar antialiasing "support" for thin polylines.
I haven't changed other methods but I do think it would make sense to make them consistent by making antialiasing not supported for width < 0 (can be done in a separate PR).

Compat-breaking because just as #69851 this PR changes the default value for width to -1.0 so the thin polylines are drawn by default (so if someone was not passing a width then now they will get unscalable thin polylines instead of the scalable ones).

Resolves #44332.
Resolves godotengine/godot-proposals#1363 (combined with #69851).

cc @dalexeev

Bugsquad edit:
Fully resolves #19844 (according to @dalexeev)

[dalexeev]

I have tested this PR, works correctly and consistent with #69851.

[clayjohn]

Looks good to me. Should be fine to merge once the error is changed to a warning (or an ERR_CONTINUE if you prefer)

[clayjohn]

Looks great!

[akien-mga]

Thanks!