Cleanup: Use DNA deprecated guards around old flags

These flags shouldn't be used except in versioning code.

Merge branch 'blender-v2.91-release'

Fix T81818: Outliner mode column crashes with shared object data

For objects with shared data, it makes sense to show the mode icon for
every object sharing the same data if one of them is in edit mode.

This also disables the "extend" functionality in this case, because
being in edit mode for multiple objects with the same data isn't
supported.

Differential Revision: https://developer.blender.org/D9273

Geometry Nodes: Add edge split node functionality

Fix T81967: Crash when using extrude on a text object

Caused by rBa308607a5334, which mistakenly removed these lines.

Fix T81909: Translation missing for some labels in modifier panels

Every label string in uiItem* calls needs an IFACE_ call.

Cleanup: Use LISTBASE_FOREACH macro in curve code

These changes should result in more readable and undestandable code,
especially where while loops were use instead of for loops. They are
not comprehensive, and I skipped wherever the change was not obvious.

Geometry Nodes: Add initial node definition for edge split

This is just based on rBa7dba81aab22, and contains no funcionality at all.

UI: Fix typo in sculpt trim tool description

Merge branch 'master' into geometry-nodes