fix(cdk/overlay): skip trigger interactions in outside click event

Adds some logic to skip the trigger when considering clicks outside of the overlay since filtering them is the most common case (e.g. we do it in some of our components) and can be annoying to deal with.

Fixes angular#28949.

src/cdk/overlay/overlay-directives.ts

@@ -27,6 +27,7 @@ import {
   booleanAttribute,
   inject,
 } from '@angular/core';
+import {_getEventTarget} from '@angular/cdk/platform';
 import {Subscription} from 'rxjs';
 import {takeWhile} from 'rxjs/operators';
 import {Overlay} from './overlay';
@@ -311,7 +312,12 @@ export class CdkConnectedOverlay implements OnDestroy, OnChanges {
     });
 
     this._overlayRef.outsidePointerEvents().subscribe((event: MouseEvent) => {
-      this.overlayOutsideClick.next(event);
+      const origin = this._getOriginElement();
+      const target = _getEventTarget(event) as Element | null;
+
+      if (!target || !origin || (origin !== target && !origin.contains(target))) {
+        this.overlayOutsideClick.next(event);
+      }
     });
   }
 
@@ -367,7 +373,7 @@ export class CdkConnectedOverlay implements OnDestroy, OnChanges {
     }));
 
     return positionStrategy
-      .setOrigin(this._getFlexibleConnectedPositionStrategyOrigin())
+      .setOrigin(this._getOrigin())
       .withPositions(positions)
       .withFlexibleDimensions(this.flexibleDimensions)
       .withPush(this.push)
@@ -379,21 +385,35 @@ export class CdkConnectedOverlay implements OnDestroy, OnChanges {
 
   /** Returns the position strategy of the overlay to be set on the overlay config */
   private _createPositionStrategy(): FlexibleConnectedPositionStrategy {
-    const strategy = this._overlay
-      .position()
-      .flexibleConnectedTo(this._getFlexibleConnectedPositionStrategyOrigin());
+    const strategy = this._overlay.position().flexibleConnectedTo(this._getOrigin());
     this._updatePositionStrategy(strategy);
     return strategy;
   }
 
-  private _getFlexibleConnectedPositionStrategyOrigin(): FlexibleConnectedPositionStrategyOrigin {
+  private _getOrigin(): FlexibleConnectedPositionStrategyOrigin {
     if (this.origin instanceof CdkOverlayOrigin) {
       return this.origin.elementRef;
     } else {
       return this.origin;
     }
   }
 
+  private _getOriginElement(): Element | null {
+    if (this.origin instanceof CdkOverlayOrigin) {
+      return this.origin.elementRef.nativeElement;
+    }
+
+    if (this.origin instanceof ElementRef) {
+      return this.origin.nativeElement;
+    }
+
+    if (typeof Element !== 'undefined' && this.origin instanceof Element) {
+      return this.origin;
+    }
+
+    return null;
+  }
+
   /** Attaches the overlay and subscribes to backdrop clicks if backdrop exists */
   private _attachOverlay() {
     if (!this._overlayRef) {