a) ImplCalcDigitLang that determines the digit language
b) ImplInitDigitMode that just sets the outputdevice according to that lang
c) and convertDigits that physically converts the digits in a string
from one language to another

then change the body of convertDigits to use GetLocalizedChar from vcl rather
than its outdated copy of the method, which teachs editeng all the digit modes
that were added since the method was originally copy and pasted.

Change-Id: I2ef7d5d3396c106d4f8fd90142c9d9cf99064bee