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.
React to aspnet/Razor#214 mvchook changes.
Fix for #1539 - We're not going to do anything special when request
services aren't enabled

This is just removing the TODO.
React to aspnet/Razor#210 changes.
Adding unit tests for HtmlHelper.Password

Partial fix for #453
TODO removal

For each of these TODOs:

- If there's an active bug tracking the work, and the TODO provides
  something of value, I left it and standardized the formatting. I also
  added comments to the bug.

- If the comment provided no value (implement feature X when we do feature
  X), I deleted it with impunity.

- If the comment was stale (won't fix or just out of date), then we
  removed it uncerimoniously.

There was a single TODO that was actually actionable, so I enabled that
test.
Fix #298 - Added ModelMetadata.Container property and unit tests.
Merge branch 'Fix298' into dev
Delete trailing whitespace
- #EngineeringDay
- Total replaced: 660  Matching files: 270 in *.cs
- Total replaced: 250  Matching files: 32 in all other files
- Total replaced: 22  Matching files: 8 in a few stragglers

Did not change files under following directories
- test\Microsoft.AspNet.Mvc.Razor.Host.Test\TestFiles\Output
- test\Microsoft.AspNet.Mvc.FunctionalTests\compiler\resources
- test\WebSites\TagHelpersWebSite
(Razor generates trailing whitespace in a case or two)
[Fixes issue #1528] default reference assemblies made extensible
- Made ReferenceAssemblies and GetCandidateLibraries virtual
- Added relevant tests
React to fallback changes
Fix flaky NoContentFormatter test
[Fixes #393] [Design] Update ViewComponent result apis to be consistent with Controller

1. Updated ViewComponent to exposes similar properties to the existing ones in controller where
appropiate. We've left out Resolver for being a bad pattern (just inject the dependency on the constructor
or use Context.RequestServices to access it if needed) and Response as although available through the Context
property, it shouldn't be used/modified in a ViewComponent.

2. Updated ViewViewComponentResult to follow a similar pattern as ViewResult where the constructor is
parameterless and elements like ViewEngine are resolved during execution if the user does not set the
associated property on the object.

3. Updated ExecuteAsync in JsonViewComponentResult to remove the unnecessary pragma and async keyword from the
signature and to use Task.FromResult(true) instead.

4. Cleaned up ViewViewComponentResult tests.