mark deprecations for mobile: extended commands such as start activity

[KazuCocoa]

E.g. https://github.com/appium/appium-uiautomator2-driver/#mobile-startactivity
As Appium client, we can gracefully mark them deprecation, and use the mobile command instead to reduce appium client specific methods

[KazuCocoa]

Not so much https://github.com/appium/ruby_lib_core/blob/master/lib/appium_lib_core/common/command.rb#L178

[KazuCocoa]

Will do more, then create a new major version that drops the deprecated methods

[KazuCocoa]

appium/java-client#2036 will be also hint