fix(cdk/listbox): avoid resetting scroll position when using mouse

The CDK listbox has some logic that forwards focus to the first item when the host is focused.
The problem is that every time the user clicks on the scrollbar, they blur the current item and focus the listbox
which then forwards focus back to the first item which in turn causes the scroll position to jump to the top.
These changes add some logic to not forward focus when focus comes from a mouse interaction.

Fixes #30900

Author: SergheiGurgurov

src/cdk/listbox/listbox.ts

@@ -9,6 +9,7 @@
 import {
   _IdGenerator,
   ActiveDescendantKeyManager,
+  FocusMonitor,
   Highlightable,
   ListKeyManagerOption,
 } from '../a11y';
@@ -243,7 +244,6 @@ export class CdkOption<T = unknown> implements ListKeyManagerOption, Highlightab
     '[attr.aria-multiselectable]': 'multiple',
     '[attr.aria-activedescendant]': '_getAriaActiveDescendant()',
     '[attr.aria-orientation]': 'orientation',
-    '(focus)': '_handleFocus()',
     '(keydown)': '_handleKeydown($event)',
     '(focusout)': '_handleFocusOut($event)',
     '(focusin)': '_handleFocusIn()',
@@ -269,6 +269,7 @@ export class CdkListbox<T = unknown> implements AfterContentInit, OnDestroy, Con
   }
   private _id: string;
   private _generatedId = inject(_IdGenerator).getId('cdk-listbox-');
+  private _focusMonitor = inject(FocusMonitor);
 
   /** The tabindex to use when the listbox is enabled. */
   @Input('tabindex')
@@ -462,6 +463,7 @@ export class CdkListbox<T = unknown> implements AfterContentInit, OnDestroy, Con
     }
 
     this._initKeyManager();
+    this._handleFocus();
 
     // Update the internal value whenever the options or the model value changes.
     merge(this.selectionModel.changed, this.options.changes)
@@ -477,6 +479,7 @@ export class CdkListbox<T = unknown> implements AfterContentInit, OnDestroy, Con
   }
 
   ngOnDestroy() {
+    this._focusMonitor.stopMonitoring(this.element);
     this._cleanupWindowBlur?.();
     this.listKeyManager?.destroy();
     this.destroyed.next();
@@ -698,15 +701,26 @@ export class CdkListbox<T = unknown> implements AfterContentInit, OnDestroy, Con
 
   /** Called when the listbox receives focus. */
   protected _handleFocus() {
-    if (!this.useActiveDescendant) {
-      if (this.selectionModel.selected.length > 0) {
-        this._setNextFocusToSelectedOption();
-      } else {
-        this.listKeyManager.setNextItemActive();
-      }
+    this._focusMonitor
+      .monitor(this.element, false)
+      .pipe(takeUntil(this.destroyed))
+      .subscribe(focusOrigin => {
+        // Don't forward focus on mouse interactions, because it can
+        // mess with the user's scroll position. See #30900.
+        if (focusOrigin === 'mouse' || focusOrigin === null) {
+          return;
+        }
 
-      this._focusActiveOption();
-    }
+        if (!this.useActiveDescendant) {
+          if (this.selectionModel.selected.length > 0) {
+            this._setNextFocusToSelectedOption();
+          } else {
+            this.listKeyManager.setNextItemActive();
+          }
+
+          this._focusActiveOption();
+        }
+      });
   }
 
   /** Called when the user presses keydown on the listbox. */