Simpler testing of libraries that are read as bytecode

For testing the interaction between source code and bytecode, such as when calling a method in bytecode from source code with the -AuseDefaultsForUncheckedCode=bytecode option turned on, there is currently no single bytecode library that is available to all JUnit tests and to which new classes can be added. It would be helpful to add a library available to all JUnit tests that is built before any JUnit tests are run. This would allow the author of code that tests such an interaction to focus on the feature being tested and not on the configuration of JUnit tests. Such a library would also make it easier to discover the set of tests that verify interactions with bytecode.

For practical reasons, there may need to be two separate bytecode libraries for Framework tests and Checker tests.

Start by inspecting the JUnit test and build configuration for the Framework and Checker tests, focusing on how test libraries are currently prepared. Done means a shared bytecode library, or separate libraries where necessary, is built before the tests run, is available to all relevant tests, and supports adding new classes.