EmulatorPkg: Add Platform CI and configuration for Core CI

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2570



Add new Azure Pipeline definitions to build and run EmulatorPkg with:
  * Ubuntu GCC5
  * Windows VS2019
Add PyTool based build of EmulatorPkg
Add EmulatorPkg.ci.yaml for Core CI
Add ReadMe.md for details and instructions

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

Reviewed-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Bret Barkelew <bret.barkelew@microsoft.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Acked-by: Ray Ni <ray.ni@intel.com>