No `@Html.Editor()` template for multiline text

[dougbu]

This is a functional gap compared to MVC 5.2. While we have all @Html.TextArea() overloads, the corresponding default editor template (MultilineTextTemplate()) does not yet exist. @Html.Editor() will return an <input> (not <textarea>) element for properties with an applied [DataType(DataType.MultilineText)].

Note bug #933 also blocks the [DataType(DataType.MultilineText)] scenario. But fixing this bug would at least allow developers to usefully set ModelMetadata.DataTypeName to "MultilineText". The scenario would work from there.

[dougbu]

Fix here is to address "MultilineText" template TODO item in TemplateRenderer and DefaultEditorTemplates.

[dougbu]

Fixed w/ commit 34f17db