[build] Enable spotbugs (#3601)

Benign spotbugs warnings were suppressed, and all others were fixed. Bug
descriptions are documented here:
https://spotbugs.readthedocs.io/en/stable/bugDescriptions.html

Co-authored-by: Austin Shalit <austinshalit@gmail.com>

wpilibjIntegrationTests/src/main/java/edu/wpi/first/wpilibj/PIDTest.java

@@ -183,6 +183,6 @@ public class PIDTest extends AbstractComsSetup {
   @Test(expected = RuntimeException.class)
   public void testOnTargetNoToleranceSet() {
     setupIntegratorRange();
-    m_controller.atSetpoint();
+    assertFalse(m_controller.atSetpoint());
   }
 }