kdevelop-msvc.bat finds VS-2017 based on a registry key on Windows.

Summary:
Some months earlier, we discussed [[ https://phabricator.kde.org/D15976 | here ]] about `kdevelop-msvc.bat` finding dynamically a VS2017 installation based on registry entries.

Although it works on my Dell laptop (Windows 7 Ultimate x64), I haven't tested it anywhere else as I don't have access to another windows machine. So... any takers?

Test Plan: In case some user has installed VS in a non-standard location (i.e. not in `C:\Program Files`), the script will be able to find the VS tools by not making the assumption that they are installed on `C:\`.

Reviewers: #kdevelop, kfunk, brauch, mwolff

Reviewed By: #kdevelop, mwolff

Subscribers: mwolff, kdevelop-devel

Tags: #kdevelop

Differential Revision: https://phabricator.kde.org/D17908