Add the following 2 APIs:
UnicodeStrnToAsciiStrS
AsciiStrnToUnicodeStrS
These APIs are used to enhance APIs UnicodeStrToAsciiStrS and
AsciiStrToUnicodeStrS (without 'n' in names) by:
1. Adds an input parameter 'Length' to specify the maximum number of
Ascii/Unicode characters to convert.
2. Adds an output parameter 'DestinationLength' to indicate the number of
Ascii/Unicode characters successfully converted.