useToolsPanel: calculate derived state in reducer to prevent too many renders (#65564)

Co-authored-by: jsnajdr <[email protected]>
Co-authored-by: youknowriad <[email protected]>
Co-authored-by: ciampo <[email protected]>
Co-authored-by: aaronrobertshaw <[email protected]>
Co-authored-by: andrewserong <[email protected]>

Author: 5 people

packages/components/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Bug Fixes
+
+-   `ToolsPanel`: atomic one-step state update when (un)registering panels ([#65564](https://github.com/WordPress/gutenberg/pull/65564)).
+
 ## 28.8.0 (2024-09-19)
 
 ### Bug Fixes