Adding STGC Overlay to 21.3 (ATLASSIM-4066)

Adding STGC overlay tools to 21.3

Also included is the RDO to Digit converters which are not currently used in STGC overlay.

This MR is the 21.3 compatible version of the STGC overlay in master !24616 (merged)

See (ATLASSIM-4066) and (ATLASSIM-4065).

MM overlay MR will be submitted after this MR is accepted.