Introduce @SentenceFragment for use with IndicativeSentences DisplayNameGenerator

[sbrannen]

Overview

While updating the Spring Framework test suite after the fixes for #4130 and #4131, I noticed that it's currently not possible to provide a custom display name for a "sentence fragment" for the IndicativeSentences DisplayNameGenerator.

You can of course register a custom DisplayNameGenerator (such as ReplaceUnderscores) to affect how a sentence fragment is generated, but you cannot provide an entire custom sentence fragment.

If you attempt to use @DisplayName for a sentence fragment, the entire sentence (that would otherwise be generated by the IndicativeSentences DisplayNameGenerator) gets overridden by the value of the @DisplayName.

As a proof of concept, I implemented @SentenceFragment and a corresponding SentenceFragmentDisplayNameGenerator) in this commit for Spring Framework's test suite.

Deliverables

• Introduce support for @SentenceFragment directly in IndicativeSentences.

[sbrannen]

PR #4349 is ready for a conceptual/technical review, in case anyone's interested. 😎