msbuild formatter should change / to \ in paths

[PeterStaev]

Bug Report

• TSLint version: 5.4.3
• TypeScript version:2.4.1
• Running TSLint via: Visual Studio

I'm using tslint withing VS Enterprise 2017 with the msbuild formatter. Although the errors get reported correctly in the Error List window if you double click on one of them it opens the file but does not go to the line where the error happens. This is because the path are using unix style slashes so they look something like:
T:/Projects/Test/test.ts
Which seems to mess up the auto navigate to the error. if the path is changed to:
T:\Projects\Test\test.ts
The correct line is opened.

[JoshuaKGoldberg]

+1 to \s on Windows. -1 to \s on Mac/Linux, which MSbuild also runs on.

The formatter should change the slash type to the native OS'.