MdeModulePkg/FileExplorer: Enable functionality of creating new file/folder

MdeModulePkg/FileExplorer: Enable functionality of creating new file/folder

https://bugzilla.tianocore.org/show_bug.cgi?id=324

Enhance the FileExplorerlib so that user can create a new file/folder
through the UI page.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>