Refactor MacVim tests and add startup delayed full screen tests #802

Job	Run time
build-and-test (macos-13, 15.2, vimtags, check-xcodeproj-compat)	4m 15s
build-and-test (macos-13, 15.2, vimtags, check-xcodeproj-compat)	4m 15s
build-and-test (macos-14, 15.4, true)	2m 53s
build-and-test (macos-14, 15.4, true)	2m 23s
build-and-test (macos-15, 16.2, true, true)	10m 40s
build-and-test (macos-15, 16.2, true, true)	10m 40s
	35m 6s

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