fix(angular/sidebar): removes -1 tabindex from sidenav in "over" mode (#2531)

Updates the sidebar component so that when the mode is not equal to `side` the tabIndex value is -1. Otherwise, provide a null value.

Author: mhaertwig

src/angular/i18n/xlf/messages.xlf

@@ -182,15 +182,15 @@
         <source>Close Sidebar</source>
         <context-group purpose="location">
           <context context-type="sourcefile">../../sidebar/sidebar/sidebar.ts</context>
-          <context context-type="linenumber">114</context>
+          <context context-type="linenumber">117</context>
         </context-group>
         <note priority="1" from="description">Button label to close the sidebar</note>
       </trans-unit>
       <trans-unit id="sbbSidebarOpenSidebar" datatype="html">
         <source>Open Sidebar</source>
         <context-group purpose="location">
           <context context-type="sourcefile">../../sidebar/sidebar/sidebar.ts</context>
-          <context context-type="linenumber">555</context>
+          <context context-type="linenumber">558</context>
         </context-group>
         <note priority="1" from="description">Button label to open the sidebar</note>
       </trans-unit>

src/angular/i18n/xlf2/messages.xlf

@@ -194,7 +194,7 @@
     </unit>
     <unit id="sbbSidebarCloseSidebar">
       <notes>
-        <note category="location">../../sidebar/sidebar/sidebar.ts:114</note>
+        <note category="location">../../sidebar/sidebar/sidebar.ts:117</note>
         <note category="description">Button label to close the sidebar</note>
       </notes>
       <segment>
@@ -203,7 +203,7 @@
     </unit>
     <unit id="sbbSidebarOpenSidebar">
       <notes>
-        <note category="location">../../sidebar/sidebar/sidebar.ts:555</note>
+        <note category="location">../../sidebar/sidebar/sidebar.ts:558</note>
         <note category="description">Button label to open the sidebar</note>
       </notes>
       <segment>

src/angular/sidebar/sidebar/sidebar.ts

@@ -98,6 +98,9 @@ export class SbbSidebarContent extends SbbSidebarContentBase implements AfterCon
     '[class.sbb-sidebar-opened]': 'opened',
     '[class.sbb-sidebar-collapsible]': 'collapsible',
     '[style.visibility]': '(!_container && !opened) ? "hidden" : null',
+    // The sidebar container should not be focused on when used in side mode.
+    // Updates tabIndex to default to null if in side mode.
+    '[attr.tabIndex]': '(mode !== "side") ? "-1" : null',
   },
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,