Recipe to simplify assertions on Optionals

[timo-abele]

What's changed?

Adds first refaster recipe

What's your motivation?

• fix assertThat(anOptional.isPresent()).isTrue() should be converted to assertThat(anOptional).isPresent() #466

Anything in particular you'd like reviewers to focus on?

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks for getting this started! As indicated in Slack as well we have two small hurdles to cross here before we can merge this in

1. support for generic over in https://github.com/openrewrite/rewrite-templating
2. allowing Java 9+ features in refaster recipes with something similar to
   • Add NoGuavaByteStreams Refaster recipe using Java 9+ rewrite-migrate-java#399
   • Inline Javatemplate in RefasterTemplateProcessor rewrite-templating#57

We're very near with all of those, so we can keep this PR open and return to it once we're ready.

[timtebeek]

I'm guessing this has since been surpassed by

• Add more simplifications #474 ?

If so we can close this one.

Thanks though! Good attempt if we were just a tad further with rewrite-templating such that generated recipes are safe to run on Java 8.

[timo-abele]

I'm guessing this has since been surpassed by

* [Add more simplifications #474](https://github.com/openrewrite/rewrite-testing-frameworks/pull/474) ?

If so we can close this one.

Thanks though! Good attempt if we were just a tad further with rewrite-templating such that generated recipes are safe to run on Java 8.

In terms of functionality this PR is obsolete. Once the blockers are resolved, rewriting the recipes currently covered by SimplifyChainedAssertJAssertion into refaster recipes would make the code more readable. Then, the code written here could be reused. But it wouldn't be much effort to write it anew either...

[timtebeek]

I'm leaning towards closing this one at least for now then, as we have some blockers to sort first, and even then there might be performance challenges to solve before we rewrite more recipes to Refaster style (as much as I like that option!).