MessageBuilder: fix typo

[stokito]

Also cleanup MessageTest

[Flowdalic]

I don't see the point in switching to String concatenation over StringBuilder. Yes, javac will probably transform String concatenation to StringBuilder and yes, one could argue it's slightly more readable. But am I not convinced that it's worth to change.

In general, please make sure that you don't conflate multiple changes within the same commit (or even, within the same PR). This makes it easier to review stuff, keeps the history clean and increases the chances for undisputed changes to land.

[stokito]

javac will probably transform String concatenation to StringBuilder and yes, one could argue it's slightly more readable

The javac will use concatenation with invokedynamic that potentially may be more optimized because pre-allocates buffer with full length. I changed the code because the IntelliJ proposed the change and it makes it automatically. There is a lot of places where the same change can be applied with one click. Similar warnings may be reported by source quality control systems like Sonarqube and this will make it easier to find more important error. It also minimizes potential errors on code change. There are other places where the IDE can refresh and improve code just automatically with 100% correctness. I just debugged the class a lot and made the cleanup for myself then decided to make a PR on it.

[Flowdalic]

I am still skeptical that switching from StringBuilder to string concat is worth it considering that we are talking about test code. That said, I agree that new code should prefer string concat over StringBuilder when sensibe.

[stokito]

I removed the commit with he StringBuilder

[Flowdalic]

I removed the commit with he StringBuilder

There is still an unrelated change in the commit

[stokito]

I fixed your comments. Also I noticed that some links to XEPs are outdated with JEP-XXXX.html. Others use http:// instead of the https://. Fixed these links and added to the PR.