refactor(cdk/overlay): test out enabling popover by default

Tries to enable popovers in the CDK overlay by default to see how hard it'll be to land.

Author: crisbeto

src/cdk/overlay/overlay-directives.ts

@@ -253,7 +253,7 @@ export class CdkConnectedOverlay implements OnDestroy, OnChanges {
 
   /** Whether the connected overlay should be rendered inside a popover element or the overlay container. */
   @Input({alias: 'cdkConnectedOverlayUsePopover'})
-  usePopover: FlexibleOverlayPopoverLocation | null = null;
+  usePopover: FlexibleOverlayPopoverLocation | null = 'global';
 
   /** Whether the overlay should match the trigger's width. */
   @Input({alias: 'cdkConnectedOverlayMatchWidth', transform: booleanAttribute})

src/cdk/overlay/overlay.ts

@@ -54,7 +54,7 @@ export function createOverlayRef(injector: Injector, config?: OverlayConfig): Ov
   const overlayConfig = new OverlayConfig(config);
 
   overlayConfig.direction = overlayConfig.direction || directionality.value;
-  overlayConfig.usePopover = !!overlayConfig?.usePopover && 'showPopover' in doc.body;
+  overlayConfig.usePopover = 'showPopover' in doc.body;
 
   const pane = doc.createElement('div');
   const host = doc.createElement('div');