Support VS2019 in Impor-VisualStudioEnvironment and so on#13

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tats-u wants to merge 4 commits intoWintellect:masterfrom

Commits on Dec 8, 2019

Add VS2019 as an option
tats-u
committed

Commits on Dec 9, 2019

Use vswhere as defaultVS2017+ contain an utility named vswhere, which discovers installed VS's.VS2019 abolished the registry that contains the infomation of the installed version.
tats-u
committed

Commits on Dec 19, 2019