[commands] Update Command documentation (NFC) (#3881)

Add reference to which VendorDep the class is included in.
Add missing OldCommands C++ Documentation (copied from Java).

wpilibNewCommands/src/main/native/include/frc2/command/button/Button.h

@@ -18,6 +18,8 @@ class Command;
  * A class used to bind command scheduling to button presses.  Can be composed
  * with other buttons with the operators in Trigger.
  *
+ * This class is provided by the NewCommands VendorDep
+ *
  * @see Trigger
  */
 class Button : public Trigger {

wpilibNewCommands/src/main/native/include/frc2/command/button/JoystickButton.h

@@ -12,6 +12,8 @@ namespace frc2 {
  * A class used to bind command scheduling to joystick button presses.  Can be
  * composed with other buttons with the operators in Trigger.
  *
+ * This class is provided by the NewCommands VendorDep
+ *
  * @see Trigger
  */
 class JoystickButton : public Button {

wpilibNewCommands/src/main/native/include/frc2/command/button/NetworkButton.h

@@ -15,6 +15,8 @@
 namespace frc2 {
 /**
  * A Button that uses a NetworkTable boolean field.
+ *
+ * This class is provided by the NewCommands VendorDep
  */
 class NetworkButton : public Button {
  public:

wpilibNewCommands/src/main/native/include/frc2/command/button/POVButton.h

@@ -12,6 +12,8 @@ namespace frc2 {
  * A class used to bind command scheduling to joystick POV presses.  Can be
  * composed with other buttons with the operators in Trigger.
  *
+ * This class is provided by the NewCommands VendorDep
+ *
  * @see Trigger
  */
 class POVButton : public Button {

wpilibNewCommands/src/main/native/include/frc2/command/button/Trigger.h

@@ -24,6 +24,8 @@ class Command;
  * methods are named fairly abstractly; for purpose-specific wrappers, see
  * Button.
  *
+ * This class is provided by the NewCommands VendorDep
+ *
  * @see Button
  */
 class Trigger {