FindGit: Avoid finding VS 2017 non-general Git installation

Brad Kingrequested to merge
brad.king/cmake:FindGit-avoid-vs-2017-git into master

At a VS 2017 command prompt the PATH contains a directory that happens to have a Git/cmd/git.exe inside it. However, this executable is not meant for general use. Revise our use of Git/ path suffixes to be more specific to its original purpose of searching in the typical c:/Program Files*/Git/ installation directories. Avoid using the suffixes on PATH entries.

Fixes: #16706 (closed)

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