Changelog for 1.31.0

[rgrunber]

• I've listed [Blocker 4.31 release] Lombok functionality doesn't work any more  #2985 as "known regression". I don't think we've ever included things we know will break into the CHANGELOG, but is there a reason not to include that (in addition pinning the issue after release) ?
• Update target platform to latest 4.31-I-builds. #2994 is mentioned twice because although it's a target platform update, it contained both some basic String templates support, and a performance improvement to "Organize Imports". Felt like the 2 deserved their own entries.

[nickzhums]

Thanks @rgrunber . We have a fairly large base of Lombok users and rolling out this release will essentially break their daily workflow. We might see people flood our Github repo with issues or some of them may just abandon VS Code. Considering our overall VS Code Java user base,, to me the cons of this regression is much bigger than the pros of other things in the changelog. I would suggest wait till we fix this issue first.

[rgrunber]

We have a solution to avoid breaking the functionality that we can implement outside of JDT-LS (client-side). Going to try it out.

[testforstephen]

LGTM