Move several E2E integration test cases to options_test

[srawlins]

Some tests in dartdoc_integration_test were flaking on the the Mac bot, timing out. I still have no idea why, but converting them to smaller tests may fix the issue (might be in processing stdout of the external application). If they're still flaky, we can diagnose them better as unit tests.

In moving these test cases, dartdoc_integration_test takes 110 fewer seconds, and options_test takes 2 more seconds.

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