MdePkg: UefiLib: Add a function to check if a language is supported

MdePkg: UefiLib: Add a function to check if a language is supported

Add a function that checks if a target language is in the supported
languages list. Add some calls to this function where appropriate in
UefiLib.c

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Tom Zhao <tzhao@solarflare.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>