Add API test coverage for 283722@main

https://bugs.webkit.org/show_bug.cgi?id=281935
rdar://138440875

Reviewed by Abrar Rahman Protyasha and Richard Robinson.

283722@main landed without any test coverage. Add an API test to help avoid
future regressions.

Verified that the test passes on main, and fails (times out) when reverting
283722@main and 283725@main (which also fixed the same issue in a different way).

* Tools/TestWebKitAPI/Tests/WebKitCocoa/WritingTools.mm:
(TEST(WritingTools, CompositionWithRestart)):

Web content crashes were encountered when performing two successive rewrites.

Add a test that makes Writing Tools API calls to match the system behavior when
performing two successive rewrites. Allow time for the animations to run to
completion.

Canonical link: https://commits.webkit.org/285590@main