GEP-16: val keyword for final declarations

Hi folks,

We have been asked numerous times about the possibility of having a "val"
keyword to match Kotlin and Scala. We also have had a related Jira open for
more than 6 years. So I created a GEP to help frame a discussion about what
would be involved and help us make a decision:

https://groovy.apache.org/wiki/GEP-16.html

I know we have "final", but many developers I speak to from the Kotlin and
Scala worlds are big fans of "val" and believe it was the right name to use
for those two languages.

Given that it involves changes to only about 15 lines of production Groovy
code and has well-identified impacts (arguably edge cases with
workarounds), I am largely in favor of this proposal, but I am keen to hear
other's thoughts.

Cheers, Paul.