UI inputs: Add input's type as a class to the parent div

This is something I have often wished existed in R-Shiny (@jcheng5 R-shiny finally makes sense, now that we have py-shiny!)

There are many cases where I want to know what type of input I'm dealing with in javascript and we always need to perform a lot of heuristic checks. It would be nice if inputs declared their own type in the parent class. For exapmle, ui.input_numeric("x", None,5) is currently

<div class="form-group shiny-input-container">
  <label class="control-label shiny-label-null" id="x-label" for="x"></label>
  <input id="x" type="number" class="form-control" value="5"/>
</div>

It could be

<div class="form-group shiny-input-container shiny-input-numeric">
  <label class="control-label shiny-label-null" id="x-label" for="x"></label>
  <input id="x" type="number" class="form-control" value="5"/>
</div>

(Stolen from https://github.com/rstudio/shiny/issues/1286)

No files or tests are named in the issue. Start by locating the code that renders Shiny input parent divs, then trace how input types are represented across the input components. Done means the relevant parent divs expose consistent type-specific classes, including the numeric example shown, with coverage for the affected inputs.