fix(sidenav): not restoring focus to SVG elements (#18614)

SVG nodes can be focusable, but they won't match `instanceof HTMLElement` so we never restore focus to them.

(cherry picked from commit 99d3e12)

src/material/sidenav/drawer.spec.ts

@@ -307,6 +307,28 @@ describe('MatDrawer', () => {
           .toBe(openButton, 'Expected focus to be restored to the open button on close.');
     }));
 
+    it('should restore focus to an SVG element', fakeAsync(() => {
+      const fixture = TestBed.createComponent(BasicTestApp);
+      fixture.detectChanges();
+
+      const drawer = fixture.debugElement.query(By.directive(MatDrawer))!.componentInstance;
+      const svg = fixture.componentInstance.svg.nativeElement;
+      const drawerButton = fixture.componentInstance.drawerButton.nativeElement;
+
+      svg.focus();
+      drawer.open();
+      fixture.detectChanges();
+      flush();
+      drawerButton.focus();
+
+      drawer.close();
+      fixture.detectChanges();
+      flush();
+
+      expect(document.activeElement)
+          .toBe(svg, 'Expected focus to be restored to the SVG element on close.');
+    }));
+
     it('should not restore focus on close if focus is outside drawer', fakeAsync(() => {
       let fixture = TestBed.createComponent(BasicTestApp);
       let drawer: MatDrawer = fixture.debugElement
@@ -907,6 +929,14 @@ class DrawerContainerTwoDrawerTestApp {
       </mat-drawer>
       <button (click)="drawer.open()" class="open" #openButton></button>
       <button (click)="drawer.close()" class="close" #closeButton></button>
+      <svg
+        viewBox="0 0 100 100"
+        xmlns="http://www.w3.org/2000/svg"
+        tabindex="0"
+        focusable="true"
+        #svg>
+        <circle cx="50" cy="50" r="50"/>
+      </svg>
     </mat-drawer-container>`,
 })
 class BasicTestApp {
@@ -920,6 +950,7 @@ class BasicTestApp {
   @ViewChild('drawer') drawer: MatDrawer;
   @ViewChild('drawerButton') drawerButton: ElementRef<HTMLButtonElement>;
   @ViewChild('openButton') openButton: ElementRef<HTMLButtonElement>;
+  @ViewChild('svg') svg: ElementRef<SVGElement>;
   @ViewChild('closeButton') closeButton: ElementRef<HTMLButtonElement>;
 
   open() {

src/material/sidenav/drawer.ts

@@ -350,7 +350,8 @@ export class MatDrawer implements AfterContentInit, AfterContentChecked, OnDestr
     const activeEl = this._doc && this._doc.activeElement;
 
     if (activeEl && this._elementRef.nativeElement.contains(activeEl)) {
-      if (this._elementFocusedBeforeDrawerWasOpened instanceof HTMLElement) {
+      // Note that we don't check via `instanceof HTMLElement` so that we can cover SVGs as well.
+      if (this._elementFocusedBeforeDrawerWasOpened) {
         this._focusMonitor.focusVia(this._elementFocusedBeforeDrawerWasOpened, this._openedVia);
       } else {
         this._elementRef.nativeElement.blur();