Make selection history global instead of per recordings

[abey79]

What

The selection history is now global, so the back/forward button work as expected when selecting various recordings.

Note (quoting my comment in the original issue):

This is technically a functional regression. Before, we could have a different selection state for each recording (e.g "/world/robot" is selected in recording A and "/world/camera" is selected in recording B). However, in practice that's no longer true since recording have been made selectable: switching to a new recording now implies selecting said recording, in turn clearing the selection. This issue would make it harder to go back to the previous behaviour.

• Fixes Selection history should be global #5736

global-selection-history.mp4

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[emilk]

With this PR, the selection history if effectively cleared when you switch recordings/apps (because none of the entities, blueprints etc in one recording exist in the other, so their Items are invalid and pruned).