fix(button): change loading button conents from div to span (#1181)

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)
- [ ] If applicable, have a visual design approval

## PR Type

What kind of change does this PR introduce?

<!-- Please check the one that applies to this PR using "x". -->

- [x] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, local variables)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Build related changes
- [ ] CI related changes
- [ ] Documentation content changes
- [ ] Other... Please describe:

## What is the current behavior?

In #1141 the loading button contents were added into a div to prevent
the button from animating on the initial render.

Issue Number: CDE-1628

## What is the new behavior?

The div is changed to a span because adding a div inside of a button is
technically not semantically correct html.

## Does this PR introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this PR contains a breaking change, please describe the impact
and migration path for existing applications below. -->

## Other information

projects/angular/src/button/button-loading/loading-button.ts

@@ -16,7 +16,7 @@ const MIN_BUTTON_WIDTH = 42;
 @Component({
   selector: 'button[clrLoading]',
   template: `
-    <div @parent [ngSwitch]="state">
+    <span @parent [ngSwitch]="state">
       <span *ngSwitchCase="buttonState.LOADING">
         <span @spinner class="spinner spinner-inline"></span>
       </span>
@@ -30,7 +30,7 @@ const MIN_BUTTON_WIDTH = 42;
       <span *ngSwitchCase="buttonState.DEFAULT" @defaultButton>
         <ng-content></ng-content>
       </span>
-    </div>
+    </span>
   `,
   providers: [{ provide: LoadingListener, useExisting: ClrLoadingButton }],
   animations: [