StdLib: Fix several problems where characters were not being correctly converted...

StdLib: Fix several problems where characters were not being correctly converted between wide and MBCS.
        Add utility functions for determining character length of strings.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by:  daryl.mcdaniel@intel.com
Reviewed-by:    erik.c.bjorge@intel.com
Reviewed-by:    lee.g.rosenbaum@intel.com
StdLib/LibC/
  Locale/multibyte_Utf8.c
    Improve comments.
    Define implementation-specific MBCS utility functions, as declared in <stdlib.h>.
    Enhance functionality of EncodeUtf8() and improve error handling.
    Set correct conversion state in wcrtomb().
    Bug fixes in wcsrtombs().
    Make wctob() properly MBCS compliant.

  Main/Main.c
    Remove code obsoleted by new wcsrtombs() implementation.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13785 6f19259b-4bc3-4df7-8a09-765794883524