This implements the main aspects of changes to blendfile compatibility
as designed in #109151:
* Blender files which file minversion is newer than current Blender
executable won't be loaded at all.
* Blender files which file version is newer than current Blender will
triger systematic warning to user:
* In the status info bar (lower right corner in default UI).
* When attempting to save (overwrite) them.
This means that the file minversion becomes a hard limit, and not a
soft, warning-only as it used to be. Further more, forward compatibility
warning is now systematic (instead of depending on file minversion),
and more visible for users.
See also https://wiki.blender.org/wiki/Process/Compatibility_Handling
for details over the new policy.
Technically:
* Opening any file with a minversion newer than current Blender file one
now triggers an early abort, with an error message reported to the user.
This is handled by a new utils called from `blo_decode_and_check`.
* Any file newer than current Blender version sets a new
`has_forward_compatibility_issues` flag in Main struct at read time.
* Status bar info area is turned into a template, which uses this flag
to display special warning UI and tooltip when set.
* A new confirmation popup appears when user tries to save (overwrite)
such a 'newer' blendfile, stating potential loos of data, and
proposing by default to 'save as' instead.
* The 'quit unsaved' popup has also been updated to 'save as' instead of
'save' when the edited file is has potential forward compitibility
issues.
Part of #109151 (PR !110109).
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