Add one-time installation of a pre-commit git hook to protect generated WPF files

[ryalanms]

This change adds a one-time installation of a pre-commit git hook to protect all of WPF's generated files. Attempts to commit changes to these files will be blocked (along with an error message).

There are two cases based on the location of Microsoft.DotNet.Arcade.Wpf.Sdk:

1. Where the restore script is called from the public GitHub site and the
   Microsoft.DotNet.Arcade.Wpf.Sdk is present in the local Git repo (e.g., dotnet-wpf/eng/wpfarcadesdk).
2. Where the restore script is called from the internal WPF repo (dotnet-wpf-int) and the
   Microsoft.DotNet.Arcade.Wpf.Sdk is in the NuGet cache (%userprofile%\.nuget\packages\microsoft.dotnet.arcade.wpf.sdk). In this case, the path to the WPF Arcade SDK is resolved at build time based on the SDK version in global.json.

For case 1, a simple poweshell script is used to install the git hook. For case 2, an inline task is called to get the tools path and install the git hook. The task consumes a property set by Sdk.props, imported by the Wpf Arcade SDK, which determines the Microsoft.DotNet.Arcade.Wpf.Sdk path at build time.
The script checks for the existence of eng/WpfArcadeSdk and/or an entry for the SDK in global.json to determine case #1 or #2.

Again, note that the build file Sdk.props needs to be imported for WpfArcadeSdkToolsDir to be set (i.e., the parameter is only available in a WPF Arcade SDK project at build time.)

[rladuca]

Looks good. I don't recall any differences from the prior hook itself, but the SDK detection looks good.