web: unit tests for the simple things, with fixes that the tests revealed (#11633)

* Added tests and refinements as tests indicate.

* Building out the test suite.

* web: test the simple things. Fix what the tests revealed.

- Move `EmptyState.test.ts` into the `./tests` folder.
- Provide unit tests for:
  - Alert
  - Divider
  - Expand
  - Label
  - LoadingOverlay
- Give all tested items an Interface and a functional variant for rendering
- Give Label an alternative syntax for declaring alert levels
- Remove the slot name in LoadingOverlay
  - Change the slot call in `./enterprise/rac/index.ts` to not need the slot name as well
- Change the attribute names `topMost`, `textOpen`, and `textClosed` to `topmost`, `text-open`, and
  `text-closed`, respectively.
  - Change locations in the code where those are used to correspond

** Why interfaces: **

Provides another check on the input/output boundaries of our elements, gives Storybook and
WebdriverIO another validation to check, and guarantees any rendering functions cannot be passed
invalid property names.

** Why functions for rendering: **

Providing functions for rendering gets us one step closer to dynamically defining our forms-in-code
at runtime without losing any type safety.

** Why rename the attributes: **

A *very* subtle bug:
[Element:setAttribute()](https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute)
automatically "converts an attribute name to all lower-case when called on an HTML element in an
HTML document." The three attributes renamed are all treated *as* attributes, either classic boolean
or stringly-typed attributes, and attempting to manipulate them with `setAttribute()` will fail.

All of these attributes are presentational; none of them end up in a transaction with the back-end,
so kebab-to-camel conversions are not a concern.

Also, ["topmost" is one word](https://www.merriam-webster.com/dictionary/topmost).

** Why remove the slot name: **

Because there was only one slot.  A name is not needed.

* Fix minor spelling error.

web/src/elements/forms/ModalForm.ts

@@ -56,7 +56,7 @@ export class ModalForm extends ModalButton {
 
     renderModalInner(): TemplateResult {
         return html`${this.loading
-                ? html`<ak-loading-overlay ?topMost=${true}></ak-loading-overlay>`
+                ? html`<ak-loading-overlay topmost></ak-loading-overlay>`
                 : html``}
             <section class="pf-c-modal-box__header pf-c-page__main-section pf-m-light">
                 <div class="pf-c-content">