ReadOnly attributes for Action, Controller, and Parameter
Update per comment
Reacting to DataProtectionServices being removed from hosting services
Merge branch 'actionmodel1495c' into dev
MVC tag helpers should not override tag name in Razor source
- #1523
- 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.
PR comments: Remove `TagHelperOutput.Merge()` extension method entirely