Revert "Revert "MSBuild support fixes""

This reverts commit 77beefd0e767d941f3d2f90eb64d2a4d68313afc.

Conflicts:
	main/src/core/MonoDevelop.Core/MonoDevelop.Projects.Formats.MSBuild/MSBuildProjectHandler.cs
Revert "Revert "[MSBuild] Implement RefreshWithContent in the v4 builder""

This reverts commit 6ec678ff6fb26e41246e9f109e40173d56029711.
[MSBuild] Fix regression when building msbuild projects

Assign the project file name when the project content is loaded from memory
instead of from a file.