Alter "Project navigation" block form to add a "View issues" button

Over at #76725-43: Refactor project issue module to use Views (G), I pointed out that the existing "Project" selector at project/issues/foo is a) confusing UI and b) going to be impossible to implement as an exposed view filter. What it's really for is to navigate you to a different project's issue queue, so let's just reuse the "Project navigate" block and add a "View issues" button there. I got this working on the plane to Boston... patch coming soon.