Blender Git Loki

Fix interger number buttons increment/decrement arrows not working in
some cases

Since rB78b56fa7d973 defining a button with 'but->a1 = 0' wasnt
automatically setting its step value to 1 in 'ui_do_but_NUM' anymore.
Instead of handling this more forgiving in 'ui_do_but_NUM', went over
the remaining cases of buttons and and defined them with a step value of
1.

Fixes T69305

Reviewed By: brecht

Maniphest Tasks: T69305

Differential Revision: https://developer.blender.org/D5631