Don't crash on binding variables.

[kelloggm]

This pull request makes it so that the Checker Framework does not crash on binding variables, but the Checker Framework still needs to properly check and type binding variables. See issue #5021.

Fixes #5013.

[kelloggm]

I've investigated the test failure here and I'm not sure how to resolve it. @smillst do you have any idea how to handle the issue described below?

The tests are failing due to a BugInCF error issued by the method testJointJavacJavaParserVisitor in BaseTypeVisitor. This issue does not occur when I run the index checker from the command line on its own; only during the tests. I think it has something to do with the processing of .ajava files.

The problem appears to be that the JointJavacJavaParserVisitor does not have any notion of what to do with a binding variable. There is a method in that class visitBindingPattern17 that I think is where such an action should take place, but it's empty and returns null. I don't know this part of the code base, so I'm not exactly certain what it is supposed to be doing - from what I can gather, it's just testing that every Javac Tree has a matching node in the JavaParser parse? But not sure how that is achieved.

Here are some possible paths forward:

• figure out what needs to go in JointJavacJavaParserVisitor#visitBindingPattern17 to make the test succeed
• disable the test in the Index Checker tests, somehow.

There are two things I'm unsure of:

• what the specification of JointJavacJavaParserVisitor#visitBindingPattern17 should be
• what the consequences of disabling this test for the Index Checker's test suite would be

[smillst]

I'll fix JointJavacJavaParserVisitor#visitBindingPattern17. I implemented JointJavacJavaParserVisitor#visitSwitchExpression17, so I know what to do.