Android: TextInput.Password should show last-typed character briefly

On Android, using echoMode:TextInput.Password in a TextField should cause the last-typed character to be shown, unmasked, for 1.5 seconds. Instead, all characters are masked.

The 1.5 seconds is hard-coded in the Android API here: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/text/method/PasswordTransformationMethod.java#242

A similar fix has already been made for iOS: https://codereview.qt-project.org/#/c/112704/