Fix undo not working in some entity drag-and-drop instances

[abey79]

This is a band-aid patch to address an issue with entity path filter which would result in the following behaviours:

• the entity path filter would be perma-writen to the blueprint store when the view is selected (in some cases)
• in such cases, this would break undo on user change (aka with entity drag-and-drop)

The core issue is deeper and might cause panics with rust 1.81+. The TL;DR is that the current EntityPathFilter type is ambiguous as to whether its content has substitutions (aka $origin) applied or not. In particular Eq and Ord apply to unsubstituted, resp. substituted content (which can lead to the above panic). This should be further cleaned by having two structures, one unsubstituted and another substituted.

[github-actions]

Web viewer failed to build.

| Result | Commit | Link | Manifest |
| ------ | ------- | ----- |
| ❌ | | https://rerun.io/viewer/pr/8526 | +nightly +main |

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