Initial introduction of DRWLayer abstraction

Used to wrap different drawing steps, i.e. the main scene drawing,
editor overlays and debug text. Later overlays should get their own
layer.
Right now only the drawing commands are wrapped into per layer
callbacks. The idea is to let each draw into different framebuffers and
to composit them together at the end, so that we can avoid redrawing all
layers if only one needs updating.

Add separate region redraw tag for UI overlays (gizmos)

Fix T73190: Anim Player button in the status bar when scrubbing

Fix view stuck at center on session start without positional tracking

Minor correction to previous commit

Fix failing asserts in versioning with some pre 2.5 files

Old pre 2.5 files may have had non active spaces stored that doen't have
a header. The 2.5 versioning only added headers for active spaces, not
inactive (so invisible) ones.
Newer versioning code assumed there to always be a header though.

Inserted a version patch to make sure there's always a header now.

Fixes error reported to Debian,
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949035.

Fix wrong usages of region align enumerations

`ARegion.alignment` unfortunately is a mixture of value and bitflag
enumerations. When checking for left/right/top/bottom region alignment,
the flags have to be masked out usually.
Most of the fixed cases here probably didn't cause issues in practice,
but could in fact break at any point when surrounding logic changes.

In fact the assert in #region_visible_rect_calc() failed in an older
file from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=949035. This
fixes it.

UI: Use same precision in "Move" redo panel as elsewhere

The floating "Move" redo panel showed transform values with less
precision than in other places (e.g. sidebar and properties editor).
With Millimeters as unit it would even round to full integers, which
may be an issue since you typically work at higher precisions with this
unit.

Note that this only applies to the visual precision, internally we use
full floating point `float`s still.

Fixes T70367.

UI: Show animation cancel button in all status-bars

Previously the button would only show up in the status-bar located in
the same window that had the screen with the animation timer.
I don't see a reason not to show the button in all status-bars instead,
other animation feedback is also displayed in all windows.

Fixes T72194.

Fix T51054: NULL-dereferences in crash-handler callback