Remove html exports and update tags

[HammadTheOne]

This PR removes direct html tag exports from the Dash R namespace, in favor of the html$tag list wrapper.

[HammadTheOne]

@daattali One annoyance here is that all the existing tests used htmlDiv instead of the new html$Div syntax. I'll work on updating them to use the new syntax.

[daattali]

Old tests should still pass. You can use internal functions in testthat unit tests. The only things that would fail is if there is dash::html* anywhere -- that wouldn't work, but that also never worked in the past since these functions were not part of the dash package until today.

And old code should also still work , because old code would explicitly load dashHtmlComponents, in which case these functions would exist.

[HammadTheOne]

@daattali I'm noticing one change in particular that I don't think is intended:

>s1 <- html$span("hmm", className = "value-output", `data-icon` = "fa-pencil")
>s2 <- html$span(children = list("hmm"), className = "value-output", `data-icon` = "fa-pencil")


>s1 
{
  "props": {
    "className": "value-output",
    "data-icon": "fa-pencil"
  },
  "type": "Span",
  "namespace": "dash_html_components",
  "propNames": ["children", "id", "n_clicks", "n_clicks_timestamp", "key", "role", "accessKey", "className", "contentEditable", "contextMenu", "dir", "draggable", "hidden", "lang", "spellCheck", "style", "tabIndex", "title", "loading_state", "data-icon"],
  "package": "dashHtmlComponents"
} 
> s2
{
  "props": {
    "children": "hmm",
    "className": "value-output",
    "data-icon": "fa-pencil"
  },
  "type": "Span",
  "namespace": "dash_html_components",
  "propNames": ["children", "id", "n_clicks", "n_clicks_timestamp", "key", "role", "accessKey", "className", "contentEditable", "contextMenu", "dir", "draggable", "hidden", "lang", "spellCheck", "style", "tabIndex", "title", "loading_state", "data-icon"],
  "package": "dashHtmlComponents"
} 

If the children property is explicitly set, it isn't passed to the children prop of the component object. However, if the string is passed without a name, it is passed to the dash component.

[daattali]

That's right, children isn't meant to be used with the html elements, instead any unnamed arguments are converted to children. All other properties are available as parameters, but children intuitively (in my opinion) makes sense to just be parameters freely given to the parent.

[HammadTheOne]

Right, I see the line here now children <- unname(content[!content_named_idx]) in tags.R.

It's interesting, and does make sense intuitively, it's just a little different from other flavors of Dash.

I'll update the tests to account for this.

[daattali]

Are you changing the tests? Old/existing tests can continue to use the original html* functions, it's completely legitimate to test them as "internal functions" in unit tests

[HammadTheOne]

I'm changing some of them, I think it makes more sense to test internal features with the same syntax that end users would be using.

That way, if something breaks in the future it'll be a little easier to trace it, rather than having to convert back and forth between syntax layers to figure out the issue.

For the most part, the test changes have been purely syntactical, to account for the tag export changes.