[Design] Add `InputTagHelper`

- first part of #1245 (mostly needs tests)
sure.  I also convinced myself any `public` configuration points (this isn't ideally a `protected` extensibility point) should be done when / if we plumb `MvcOptions` into `HtmlHelper` and our various `ITagHelper` implementations e.g. `ViewContext.ClientValidationEnabled`, `ViewContext.Html5DateRenderingMode`, `DefaultHtmlGenerator.IdAttributeDotReplacement`, `TemplateRenderer._defaultDisplayActions`, `TemplateRenderer._defaultEditorActions`, and this should get defaults or additions from `MvcOptions`.