BaseTools:Add DetectNotUsedItem.py to Edk2\BaseTools\Scripts

BaseTools:Add DetectNotUsedItem.py to Edk2\BaseTools\Scripts

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=1850

This script is used to Detect unreferenced PCD and GUID/Protocols/PPIs.
The input parameters are Dec file and package directory.

This script can be run in both Py2 and Py3.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>