feat(themes): add support for modular themes and custom themes #16922

Job	Run time
build-core	1m 37s
test-core-clean-build	12s
test-core-lint	55s
test-core-spec	42s
build-angular	1m 1s
build-angular-server	31s
build-react	54s
test-core-screenshot (2, 20)	10m 40s
test-core-screenshot (4, 20)	11m 32s
build-vue	40s
test-core-screenshot (6, 20)	10m 4s
test-core-screenshot (3, 20)	9m 12s
test-core-screenshot (5, 20)	9m 53s
test-core-screenshot (1, 20)	10m 20s
test-core-screenshot (17, 20)	9m 40s
test-core-screenshot (16, 20)	7m 27s
test-core-screenshot (7, 20)	3m 8s
test-core-screenshot (9, 20)	4m 59s
test-core-screenshot (18, 20)	8m 58s
test-core-screenshot (20, 20)	4m 8s
test-core-screenshot (8, 20)	4m 48s
test-core-screenshot (15, 20)	10m 4s
test-core-screenshot (12, 20)	4m 35s
test-core-screenshot (13, 20)	6m 40s
test-core-screenshot (14, 20)	6m 46s
test-core-screenshot (19, 20)	7m 17s
test-core-screenshot (11, 20)	5m 45s
test-core-screenshot (10, 20)	4m 25s
build-vue-router	37s
build-react-router	32s
test-angular-e2e (ng19)	4m 6s
test-angular-e2e (ng16)	4m 13s
test-angular-e2e (ng17)	4m 17s
test-angular-e2e (ng20)	4m 14s
test-angular-e2e (ng18)	4m 13s
test-vue-e2e (vue3)	3m 25s
test-react-e2e (react18)	3m 25s
test-react-e2e (react17)	3m 26s
test-react-e2e (react19)	2m 55s
test-react-router-e2e (reactrouter5)	3m 2s
verify-test-react-router-e2e	2s
verify-test-vue-e2e	2s
verify-test-react-e2e	4s
verify-test-angular-e2e	3s
verify-screenshots	2s
	3h 15m 31s

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