[MSBuild] Minor cleanup
[MSBuild] Send more MSBuild error details back to MD

End line/col, help keywords etc - though we don't use it yet.
[MSBuild] Report invalid project errors when using new engine
[MSBuild] Log project file error to build output
[Ide] Formatting commands should use document's mimetype

Instead of looking it up again.
[Xml] No longer need to special-case format command

The default implementation will now respect the editor's overidden
mimetype.
[Ide] Add MSBuild mimetype for targets files
Fix bizarre dependencies in CompletionCharacters extension point

There's no good reason for these extensions to have an explicit ordering,
and the insertbefore/after attributes introduced some backwards
and strange dependencies, making XmlEditor, CSharpBinding, CBinding
effectively dependent on AspNet.
[Xml] Minor cleanup
[Ide] Slightly optimize creating TextEditorExtension chain
[Xml] Added simple MSBuild code completion