refactor(material/sidenav): updates syntax

Updates previous fix to use proper syntax to calculate which
mode that the sidenav is set to.

Author: essjay05

src/material/sidenav/drawer.ts

@@ -165,7 +165,7 @@ export class MatDrawerContent extends CdkScrollable implements AfterContentInit
     // this was also done by the animations module which some internal tests seem to depend on.
     // Simulate it by toggling the `hidden` attribute instead.
     '[style.visibility]': '(!_container && !opened) ? "hidden" : null',
-    'tabIndex': '(mode !== "side") ? "-1" : null',
+    '[attr.tabIndex]': '(mode !== "side") ? "-1" : null',
   },
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,

src/material/sidenav/sidenav.ts

@@ -47,7 +47,7 @@ export class MatSidenavContent extends MatDrawerContent {}
   templateUrl: 'drawer.html',
   host: {
     'class': 'mat-drawer mat-sidenav',
-    'tabIndex': '-1',
+    '[attr.tabIndex]': '(mode !== "side") ? "-1" : null',
     // must prevent the browser from aligning text based on value
     '[attr.align]': 'null',
     '[class.mat-drawer-end]': 'position === "end"',