This fixes a problem where we'd build the same project reference from
dotnet-shared.csproj in parallel, and each build would stomp on eachother
(because we'll now clone the project references in dotnet-shared.csproj).
This als required updating project files to use MSBuildThisFileDirectory
instead of MSBuildProjectDirectory, which makes it easier for xharness to
inline/process these files, because MSBuildThisFileDirectory is easy to know
when processing a file, while MSBuildProjectDirectory depends on the calling
project, which complicates matters significantly.
A fix in MonoTouch.Dialog was also required.
New commits in migueldeicaza/MonoTouch.Dialog:
* migueldeicaza/MonoTouch.Dialog@59fbf5b [dotnet] Shared project files don't need the DefaultTargets/ToolsVersion/xmlns attributes.
Diff: 4d0e0a9a5f..59fbf5bb1b
Fixes https://github.com/xamarin/maccore/issues/2527.
bc2a5e2251