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>

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/CommandDecoratorTest.java

@@ -168,6 +168,7 @@ class CommandDecoratorTest extends CommandTestBase {
     }
   }
 
+  @SuppressWarnings("removal") // Command.perpetually()
   @Test
   void perpetuallyTest() {
     try (CommandScheduler scheduler = new CommandScheduler()) {
@@ -184,6 +185,22 @@ class CommandDecoratorTest extends CommandTestBase {
     }
   }
 
+  @Test
+  void endlesslyTest() {
+    try (CommandScheduler scheduler = new CommandScheduler()) {
+      Command command = new InstantCommand();
+
+      Command perpetual = command.endlessly();
+
+      scheduler.schedule(perpetual);
+      scheduler.run();
+      scheduler.run();
+      scheduler.run();
+
+      assertTrue(scheduler.isScheduled(perpetual));
+    }
+  }
+
   @Test
   void unlessTest() {
     try (CommandScheduler scheduler = new CommandScheduler()) {

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/EndlessCommandTest.java

@@ -0,0 +1,23 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.wpilibj2.command;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class EndlessCommandTest extends CommandTestBase {
+  @Test
+  void endlessCommandScheduleTest() {
+    try (CommandScheduler scheduler = new CommandScheduler()) {
+      EndlessCommand command = new EndlessCommand(new InstantCommand());
+
+      scheduler.schedule(command);
+      scheduler.run();
+
+      assertTrue(scheduler.isScheduled(command));
+    }
+  }
+}

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/ParallelRaceGroupTest.java

@@ -137,8 +137,8 @@ class ParallelRaceGroupTest extends CommandTestBase {
     Command command1 = command1Holder.getMock();
     MockCommandHolder command2Holder = new MockCommandHolder(true, system2);
     Command command2 = command2Holder.getMock();
-    MockCommandHolder perpetualCommandHolder = new MockCommandHolder(true);
-    Command command3 = new PerpetualCommand(perpetualCommandHolder.getMock());
+    MockCommandHolder endlessCommandHolder = new MockCommandHolder(true);
+    Command command3 = new EndlessCommand(endlessCommandHolder.getMock());
 
     Command group1 = new SequentialCommandGroup(command1, command2);
     assertNotNull(group1);

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/PerpetualCommandTest.java

@@ -9,6 +9,7 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
 import org.junit.jupiter.api.Test;
 
 class PerpetualCommandTest extends CommandTestBase {
+  @SuppressWarnings("removal") // PerpetualCommand
   @Test
   void perpetualCommandScheduleTest() {
     try (CommandScheduler scheduler = new CommandScheduler()) {

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/ScheduleCommandTest.java

@@ -36,7 +36,7 @@ class ScheduleCommandTest extends CommandTestBase {
           new SequentialCommandGroup(new InstantCommand(), scheduleCommand);
 
       scheduler.schedule(group);
-      scheduler.schedule(new InstantCommand().perpetually());
+      scheduler.schedule(new InstantCommand().endlessly());
       scheduler.run();
       assertDoesNotThrow(scheduler::run);
     }