To update from "Data saver" to "Data Saver"

To change data_saver_title res string from "Data saver" to "Data Saver".
There are 2 places to change and most of them are belong to en locale
charactors.
  res/values/strings.xml
    To change XML To "Help URL, Data saver" to "Help URL, Data Saver"
    because there is already one XML comment "Data Saver mode is on".
    To change data_saver_title to be "Data Saver" because
    condition_bg_data_title use "Data Saver".

Bug: 75983079
Test: make -j SettingsRoboTests RunSettingsRoboTests
Change-Id: I4ef88c962d6388c38841d47e4dc9674e8a4bb793