pgsql: Add support for Visual Studio 2019 in build scripts

Add support for Visual Studio 2019 in build scripts

This fixes at the same time a set of inconsistencies in the
documentation and the scripts related to the versions of Windows SDK
supported.

Author: Haribabu Kommi
Reviewed-by: Andrew Dunstan, Juan José Santamaría Flecha, Michael
Paquier
Discussion: https://postgr.es/m/CAJrrPGcfqXhfPyMrny9apoDU7M1t59dzVAvoJ9AeAh5BJi+UzA@mail.gmail.com
Backpatch-through: 9.4

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f2d069ce95b13f7ebfc4998ed708e3693166f46d

Modified Files
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doc/src/sgml/install-windows.sgml | 20 ++++++++------
src/tools/msvc/MSBuildProject.pm  | 25 +++++++++++++++++
src/tools/msvc/README             | 14 +++++-----
src/tools/msvc/Solution.pm        | 28 +++++++++++++++++++
src/tools/msvc/VSObjectFactory.pm | 58 +++++++++++++++++++++++++++++----------
5 files changed, 114 insertions(+), 31 deletions(-)