[commands] Update Subsystem factories and example to return CommandBase (#4729)

Also update rapidreactcommandbot example factories to fit this convention (as in #4655).

C++ does not need an update as CommandPtr already uses CommandBase (#4677).

wpilibNewCommands/src/main/java/edu/wpi/first/wpilibj2/command/Subsystem.java

@@ -85,7 +85,7 @@ public interface Subsystem {
    * @return the command
    * @see InstantCommand
    */
-  default Command runOnce(Runnable action) {
+  default CommandBase runOnce(Runnable action) {
     return Commands.runOnce(action, this);
   }
 
@@ -97,7 +97,7 @@ public interface Subsystem {
    * @return the command
    * @see RunCommand
    */
-  default Command run(Runnable action) {
+  default CommandBase run(Runnable action) {
     return Commands.run(action, this);
   }
 
@@ -110,7 +110,7 @@ public interface Subsystem {
    * @return the command
    * @see StartEndCommand
    */
-  default Command startEnd(Runnable start, Runnable end) {
+  default CommandBase startEnd(Runnable start, Runnable end) {
     return Commands.startEnd(start, end, this);
   }
 
@@ -122,7 +122,7 @@ public interface Subsystem {
    * @param end the action to run on interrupt
    * @return the command
    */
-  default Command runEnd(Runnable run, Runnable end) {
+  default CommandBase runEnd(Runnable run, Runnable end) {
     return Commands.runEnd(run, end, this);
   }
 }