Fully support switch expressions

[smillst]

#4976 makes it so that the Checker Framework doesn't not crash on switch expressions, but it does not handle them as precisely as possible. Here's a list of TODOs to finish supporting switch expressions:

• TypeFromExpressionVisitor.java: Correctly compute the type of switch expressions. (Compute the type of switch expressions and check them. #4978)
• BaseTypeVisitor.java: Check that the type of the result expressions of the switch expression are subtypes of the type of the switch expression. (Compute the type of switch expressions and check them. #4978)
• CFGTranslationPhaseOne.java : analyze switch expressions. (Add support for switch expressions in dataflow #4982)
• BaseTypeVisitor.java: JointJavacJavaParserVisitor needs to be updated to handle switch expressions. (JointJavacJavaParserVisitor now handles switch expressions  #4992)

[msridhar]

@Gellert5225 has started looking into handling arrow case labels in switch statements, but he is not looking at switch expressions. When I spoke to @mernst we decided the work for statements and expressions could be done somewhat in parallel, but if you think closer coordination is warranted, let us know and we can discuss further.

[smillst]

CFGTranslationPhaseOne.SwitchBuilder needs to be update to handle the arrow case labels. I think support for switch expressions will use the updated switch builder. (I say "think", because Mike and I haven't settled on an implementation strategy yet.). However, we can probably work on support for switch expressions before SwitchBuilder is updated by just using test cases that use case L : <block> or case : -> <expression> varieties.

[msridhar]

Ok, sounds good, @Gellert5225 and I will communicate / open PRs as we make progress.

[smillst]

All the tasks have been fixed, so I'm closing this issue.