[Unit tests] Fix path of Java bindings (#6616)

[Unit tests] Fix path of Java bindings (#6616)

Currently, when configuring cvc5 with Java bindings, CMake complains
about `get_filename_component(CVC5_JNI_PATH ${CVC5_JAR_PATH} DIRECTORY)`
not using the correct number of arguments in the Java unit tests. The
issue is that `${CVC5_JAR_PATH}` is empty. The value of
`${CVC5_JAR_PATH}` was computed in the Java API bindings but then not
shared with the rest of the build system. Because `${CVC5_JAR_PATH}` is
not used anywhere else, this commit moves the computation of
`${CVC5_JAR_PATH}` to the unit tests. The commit also ensures that the
API subdirectories are processed before the test subdirectories.