This fixes T68521, T82334.
The object are not properly mirrored in object mode.
For mirroring an object that has an arbitrary rotation along the X axis
this is the procedure:
1. mirror x location.
2. negate x scale of the
3. negate y and z component of the rotation (independent of which rotation mode is used).
This knowledge applies now for all angles and axes to finally make the
mirror operation work in object mode.
The new mirror function has the downside that it can not (in this form)
be used with proportional editing.
This is no problem since the old behavior can still be replicated by
scaling with -1 along any axis.
The solution to get perfect mirrors can not work for scaling in general,
because in that case there could be scew created.
Reviewed By: mano-wii
Differential Revision: https://developer.blender.org/D9625
This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.
This patch has been generated by P1561 followed by `make format`.
Differential Revision: https://developer.blender.org/D8466
