dropdown: add optional sync property to align popup width to trigger slot element width (#1935)

Co-authored-by: Nic Newdigate <nic.newdigate@vivantio.com>

src/components/dropdown/dropdown.component.ts

@@ -3,6 +3,7 @@ import { classMap } from 'lit/directives/class-map.js';
 import { getAnimation, setDefaultAnimation } from '../../utilities/animation-registry.js';
 import { getTabbableBoundary } from '../../internal/tabbable.js';
 import { html } from 'lit';
+import { ifDefined } from 'lit/directives/if-defined.js';
 import { LocalizeController } from '../../utilities/localize.js';
 import { property, query } from 'lit/decorators.js';
 import { waitForEvent } from '../../internal/event.js';
@@ -102,6 +103,11 @@ export default class SlDropdown extends ShoelaceElement {
    */
   @property({ type: Boolean }) hoist = false;
 
+  /**
+   * Syncs the popup width or height to that of the trigger element.
+   */
+  @property({ reflect: true }) sync: 'width' | 'height' | 'both' | undefined = undefined;
+
   connectedCallback() {
     super.connectedCallback();
 
@@ -409,6 +415,7 @@ export default class SlDropdown extends ShoelaceElement {
         shift
         auto-size="vertical"
         auto-size-padding="10"
+        sync=${ifDefined(this.sync ? this.sync : undefined)}
         class=${classMap({
           dropdown: true,
           'dropdown--open': this.open