Proposal: DependsOnTask for project items Include

For `Problem statement` and `Part 1`, see https://github.com/Microsoft/msbuild/issues/3219

Part 2:

```xml

```

this will indicate the design-time or first-evaluation-time to run the task before evaluating this line, ignore the task result and continue evaluation once task is finished. If task fails (due to insufficient credentials / no internet connection / wrong URL / any other reason), a reason warning will be issued and subsequent steps will fail as they fail today:

> CSC : error CS2001: Source file 'C:\testproj\nonexisting.cs' could not be found.

for `` and for ``

> error : File not found: 'C:\testproj\mockimage.png'

etc.