Segments size in ConcavePolygonShape2D can't be set via mouse

[qarmin]

Godot version:
3.2 123edd0

OS/device including version:
Ubuntu 19.04

Issue description:
I can't change segments size in ConcavePolygonShape2D via mouse, because every time when I try to do this this error is shown:

servers/physics_2d/shape_2d_sw.cpp:910 - Condition ' len % 2 ' is true.

Writing from keyboard works great.
Probably this field should have step with size 2, to prevent error spam when changing this values.

Steps to reproduce:

1. create collision shape
2. Set as shape ConcavePolygonShape2D
3. Try to set segments size via mouse or keyboard

[Raphael2048]

Seems that concave polygon size can only be even, don't know why be designed like this.

[Xrayez]

Not sure if there's really a need to modify vertices via inspector, this just needs a polygon editor (just like you can edit Polygon2D, CollisionPolygon2D etc).

The idea of making convex and concave polygons consistent is preliminary rejected in #32979 (comment), so the only way to fix this issue now is:

• allowing to set an array of any size, without removing the error message;
• making an editor to modify those shapes in CollisionShape2D, see ConvexPolygonShape2D can't be edited with mouse like CollisionPolygon2D #21394.
• modifying the inspector behavior to add 2 vertices in a single step, as suggested in the issue.