Help: Add MSVC_TOOLSET_VERSION value for v143 toolset
This change was missed in !6497 (merged).
Backport: release
Topic-rename: doc-MSVC_TOOLSET_VERSION-v143
Edited by Brad King
This change was missed in !6497 (merged).
Backport: release
Topic-rename: doc-MSVC_TOOLSET_VERSION-v143