Add default statementDefinition() methods
Ever since Java 8 we can implement methods as default, which is
a perfect fit for our representation classes. Make sure all migrated
statements provide this method, making our life easier on the class
design side -- as we do not need to capture/copy those statements.
Also remove AbstractBooleanDeclaredStatement, as it serves no real
purpose except to split our class hierarchy.
JIRA: YANGTOOLS-1065
Change-Id: I707bf842964748f98b5062d65cffc1e8b8fb421d
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
98948981ae99dd0a8366908c7448b5b7de0584d3)
(cherry picked from commit
4ba56f39dc90569c2600bbb7ea213b17b6b40461)