windows: test for msvs_shard and support in ninja

Main code moved from msvs.py to MSVSUtil.py (named to correspond with the rest of the MSVS helper files), and then also used in the ninja generator.

Functionality was not tested before afaict, so added a simple test that uses msvs_shard in the same way Chromium uses it (on a static_library target).

BUG=chromium:166201
Review URL: https://codereview.chromium.org/12208026

git-svn-id: http://gyp.googlecode.com/svn/trunk@1569 78cadc50-ecff-11dd-a971-7dbc132099af