feat: Add API method CtAbstractSwitch.addCaseAt

[algomaster99]

Reference: #3884 (comment).

[algomaster99]

I had a few questions, a little unrelated to this PR, about two APIs in CtCase - setCaseExpression and addCaseExpression. What is the difference between their purposes? As far as I can see, the former modifies this.caseExpressions while the latter modifies this.caseExpression. Do we need to have the attribute this.caseExpression? I understand before Java 12 only one expression was allowed per case so maybe that's why this.caseExpression exists but now we can implement setCaseExpression to clear the list and just add one expression to the list of case expressions. Similary, getCaseExpression can just return the first element of the list.

I was using the setCaseExpression before and was trying to pretty-print CtCase after that but I did not see any expression in there because the visitor doesn't even look for this.caseExpression. The above suggestion can help resolve this.

[monperrus]

LGTM, will merge ;)

[algomaster99]

@monperrus squash and merge it because some of the commits in between don't pass the CI tests so we don't want to break the master at any point. Moreover, the commit messages don't follow the spoon conventions too but the PR title does.

[slarse]

@algomaster99 We always squash :)

[slarse]

I understand before Java 12 only one expression was allowed per case so maybe that's why this.caseExpression exists but now we can implement setCaseExpression to clear the list and just add one expression to the list of case expressions.

Agree, open a separate issue/PR about that.

[monperrus]

Thanks a lot @algomaster99