Add VS2019 Toolchain def

Add VS2019 Toolchain def

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2182

In order to support VS2019,
the first thing need to do is add 2019 toolchain on tools_def.template

v2: add ARM/AARCH64/EBC Definitions, Combine VS2017_HOST and VS2019_HOST to VS_HOST

Cc: Amy Chan <amy.chan@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Ching JenX Cheng <ching.jenx.cheng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Pete Batard <pete@akeo.ie>