Media: A11y: Remove tabindex on tabpanels.

Tabindex should be set on a tabpanel if there is content in that tabpanel that is not focusable. The media library uses tabpanels, but the first content is either focusable or redundant.

Change the media library tabpanels to omit tabindex attributes.

Props alh0319, joedolson, westonruter, huzaifaalmesbah.
Fixes #63984.

git-svn-id: https://develop.svn.wordpress.org/trunk@61626 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/js/media/views/media-frame.js

@@ -101,7 +101,7 @@ MediaFrame = Frame.extend(/** @lends wp.media.view.MediaFrame.prototype */{
 			tabPanelEl = this.$el.find( '.media-frame-tab-panel' ),
 			ariaLabelledby;
 
-		tabPanelEl.removeAttr( 'role aria-labelledby tabindex' );
+		tabPanelEl.removeAttr( 'role aria-labelledby' );
 
 		if ( this.state().get( 'menu' ) && this.menuView && this.menuView.isVisible ) {
 			ariaLabelledby = 'menu-item-' + stateId;
@@ -111,7 +111,6 @@ MediaFrame = Frame.extend(/** @lends wp.media.view.MediaFrame.prototype */{
 				.attr( {
 					role: 'tabpanel',
 					'aria-labelledby': ariaLabelledby,
-					tabIndex: '0'
 				} );
 		}
 	},
@@ -127,7 +126,7 @@ MediaFrame = Frame.extend(/** @lends wp.media.view.MediaFrame.prototype */{
 		var tabPanelEl = this.$el.find( '.media-frame-content' ),
 			ariaLabelledby;
 
-		tabPanelEl.removeAttr( 'role aria-labelledby tabindex' );
+		tabPanelEl.removeAttr( 'role aria-labelledby' );
 
 		// Set the tab panel attributes only if the tabs are visible.
 		if ( this.state().get( 'router' ) && this.routerView && this.routerView.isVisible && this.content._mode ) {
@@ -137,7 +136,6 @@ MediaFrame = Frame.extend(/** @lends wp.media.view.MediaFrame.prototype */{
 				.attr( {
 					role: 'tabpanel',
 					'aria-labelledby': ariaLabelledby,
-					tabIndex: '0'
 				} );
 		}
 	},