Add assertions for JDK YearMonth type

[tmvlpl]

Check List:

• Fixes Assertions for JDK YearMonth Type #3141
• Unit tests : YES
• Javadoc with a code example (on API only) : YES

This PR adds assertions for the java.time.YearMonth type. I have based the new assertions on the existing LocalDate assertions. Therefore they should contain similar/matching assertions except for the following differences:

• no hasDayOfMonth assertion
• no isToday assertion
• an isCurrentYearMonth assertion

I hope I found and extended all the right entry points.

[tmvlpl]

I'm wondering if there is anything I can do in light of the failing pitest check, although it seems to be related to some license issue?

[scordio]

Nothing to be done, @tmvlpl, and yes, it's a license issue (see #3140).

[goughy000]

Hey this looks great - looks like the PR has been open a while though. @scordio - do you know if there's anything outstanding before the team can get this merged and released?

[scordio]

@goughy000 we'll need to review the changes so it's mostly a matter of time 🙂 I'll add it to the 3.26.0 milestone.

[tmvlpl]

The 3.25.0 release added isInThePast and isInTheFuture to the missing Java 8 date/time types. These could be added for YearMonth too. I can try to rebase the branch this weekend and add the two new assertions.

[tmvlpl]

The PR already contained the two new methods. So I only rebased it and updated the Javadoc tags.

[joel-costigliola]

Integrated thanks @tmvlpl !