fix(SplitterLayout): implement latest design specs #19325

Job	Run time
reuse-compliance	8s
Install Dependencies	1m 11s
check-bundle-size	4m 18s
Build (18)	1m 48s
Build (19)	2m 21s
lint	1m 40s
test / Cypress (base, 18)	2m 46s
test / Cypress (base, 19)	2m 8s
test / Cypress (charts, 18)	4m 15s
test / Cypress (charts, 19)	3m 46s
test / Cypress (cypress-commands, 18)	2m 26s
test / Cypress (cypress-commands, 19)	1m 43s
test / Cypress (main/src/components, 18)	6m 17s
test / Cypress (main/src/components, 19)	5m 53s
test / Cypress (main/src/internal, 18)	2m 33s
test / Cypress (main/src/internal, 19)	1m 43s
test / Cypress (compat, 18)	2m 44s
test / Cypress (compat, 19)	1m 48s
deploy-next-docs	0s
test / Combine Coverage	2s
	49m 30s

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