ShellPkg/ShellProtocol.c: Fix case sensitivity in GetAlias and SetAlias

ShellPkg/ShellProtocol.c: Fix case sensitivity in GetAlias and SetAlias

ShellCommandIsOnAliasList is case insensitive, but GetAlias and SetAlias use the
UEFI variable services, which are case sensitive.

Force alias names to lowercase to get around this.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brendan Jackman <Brendan.Jackman@arm.com>
Reviewed-By: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Jaben Carsey <Jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15270 6f19259b-4bc3-4df7-8a09-765794883524