This refactors 3 functions out of ShellCommandLib and puts them into a new library...

This refactors 3 functions out of ShellCommandLib and puts them into a new library (but as 2 functions instead of 3).  This allows for users outside of the shell itself to have access to these functions.

1) Remove the 3 functions out of the shell's internal library (ShellCommandLib)
2) Add a new library class (PathLib)
3) Add an instance of this class (BasePathLib)
4) Change all internal shell callers to use this new library class.

signed-off-by: jcarsey
reviewed-by: jljusten

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11936 6f19259b-4bc3-4df7-8a09-765794883524