Fix: Resource: Make set_path() resilient to stale cache entries

[channesl]

Fixes #112164

Fixes an editor error when a file moved outside the editor is moved back inside the editor. Resource::set_path() is made tolerant of harmless cache collisions so the reassignment doesn’t fail with:

ERROR: Another resource is loaded from path 'res://1.gd' (possible cyclic resource inclusion).

What changed:

• If the cached entry at p_path is the same object: allow (no-op).
• If p_take_over == true: evict old entry (unchanged behavior).
• If the existing entry has no external owners (refcount <= 1): auto-evict as stale.
• Editor-only (TOOLS_ENABLED): if the new resource has no path yet, allow takeover to reconcile stale editor state.
• Runtime/export behavior remains strict and unchanged.

External moves can leave a stale ResourceCache entry for the old path. Reassigning the path then collides with that stale entry. The above rules safely evict stale entries (and, in editor builds, resolve transient references) to avoid false errors.