Modified dumpsys user so it always shows config_multiuserMaximumUsers

Currently, it just dumps UM.getMaxSupportedUsers(), which uses the
config but also read fw.max_users; with this change, it will show
both values when overridden. Example:

$ adb shell dumpsys user | grep "Max user"
  Max users: 4 (limit reached: false)

$ adb shell setprop fw.max_users 42 && adb shell dumpsys user | grep "Max user"
  Max users: 42 (built-in value: 4) (limit reached: false)

Bug: 397907533
Test: manual verification (see above)
Flag: EXEMPT changes on debugging components only

Change-Id: I5733cb7bf22cb9f60a45c14cb54e0df625322b34