Fix internal deprecation warnings (#4257)

This allows us to error out on deprecation warnings for thirdparty
libraries and standard library features.

Co-authored-by: Starlight220 <53231611+Starlight220@users.noreply.github.com>

wpilibj/src/test/java/edu/wpi/first/wpilibj/simulation/EncoderSimTest.java

@@ -69,6 +69,7 @@ class EncoderSimTest {
     }
   }
 
+  @SuppressWarnings("deprecation") // Encoder.getPeriod()
   @Test
   void testPeriod() {
     HAL.initialize(500, 0);