ReadOnly attributes for Action, Controller, and Parameter
Update per comment
Merge branch 'actionmodel1495c' into dev
changed contract.assert to debug.assert
Fix for #1194 - Error using [HttpPost] and [Route] together

This change enables some compatibility scenarios with MVC 5 by expanding
the set of legal ways to configure attribute routing. Most promiently, the
following example is now legal:

[HttpPost]
[Route("Products")]
public void MyAction() { }

This will define a single action that accepts POST on route "Products".

See the comments in #1194 for a more detailed description of what changed
with more examples.
Checkin VS modifications to kproj

My up-to-date VS wants these projects to have port numbers. Makes sense
because they are web projects.
MVC tag helpers should not override tag name in Razor source
- #1523
- remove `TagHelperOutput.Merge()` extension method entirely
- test tag name preservation with all MVC tag helpers
 - `<input/>` tag helper generation of a checkbox wasn't previously tested

nits:
- fix argument order in a couple of `Assert.Equal()` calls
- remove use of "original tag name"
Address small `InputTagHelper` bug discovered while testing
- Type attribute value was "Type", not "type", when determined from template hints

nit: remove useless condition
Add more tests of `<input/>` tag helper
- scenarios where helper takes different code paths were not well-explored

nits:
- improve a few comments and names
- refactor some setup code into helper methods
- use `EmptyModelMetadataProvider`, not `DataAnnotationsModelMetadataProvider`

Test gap around `GenerateTextBox()`'s `format` argument is temporary.
React to aspnet/Razor#214 changes.

- TagHelperAttributeDescriptors changed to be lighterweight and not depend on PropertyInfo, had to modify our use of them to work with the new contract.