Add support for third-party GUI framework plugins #3560

Job	Run time
Check towncrier / Towncrier Checks	49s
Python package / Create Python Package	1m 25s
Pre-commit checks / Pre-commit Checks	39s
Unit tests (macos, 3.8)	1m 51s
Unit tests (macos, 3.9)	1m 34s
Unit tests (macos, 3.10)	1m 41s
Unit tests (macos, 3.11)	2m 7s
Unit tests (macos, 3.12)	2m 17s
Unit tests (ubuntu, 3.8)	2m 12s
Unit tests (ubuntu, 3.9)	1m 9s
Unit tests (ubuntu, 3.10)	1m 12s
Unit tests (ubuntu, 3.11)	2m 12s
Unit tests (ubuntu, 3.12)	3m 5s
Unit tests (windows, 3.8)	3m 46s
Unit tests (windows, 3.9)	3m 26s
Unit tests (windows, 3.10)	2m 20s
Unit tests (windows, 3.11)	2m 18s
Unit tests (windows, 3.12)	3m 53s
Unit tests (windows, winstore3.12, false)	4m 37s
Project coverage	25s
Build app	0s
	42m 58s

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