Refactor IsCamelCapsTest to use dataproviders

[jrfnl]

The PHP_CodeSniffer\Util\Common::isCamelCaps() method is fully covered by dedicated tests in the IsCamelCapsTest class, however, those tests don't comply with certain best practices:

• Multiple assertions in each test method.
• No failure description for assertions when a test contains multiple assertions.
• Unrelated failing assertion can block other tests from running.

The short of it is that these tests could be improved by being refactored to simple test methods containing a single assertion in combination with data providers with descriptively named data sets.

As part of the refactor, a critical look at whether the test cases included are sufficient wouldn't be a bad thing, as code coverage doesn't tell the whole story.