Unpack WPF sources

[AustinWise]

When the WPF source code was added by #229, it was in the form a single ZIP file. It would be nice if the individual source files were checked into this repo, like all the other source code in this repo. I ran the following commands to generate this pull request:

cd wpf
unzip src.zip
rm src.zip
git add .
env GIT_COMMITTER_NAME=dotnet-bot GIT_AUTHOR_NAME=dotnet-bot GIT_COMMITTER_EMAIL=dotnet-bot@microsoft.com GIT_AUTHOR_EMAIL=dotnet-bot@microsoft.com git commit -m "Unpack WPF sources"

I know this repository is documented as not accepting pull requests. But maybe someone from Microsoft can use the above commands to recreate this commit and add the sources.

[AustinWise]

@harshit7962 It would be nice if you could check in the source files of WPF instead a ZIP file of it.