Update mouse button pressed state when setting capture

This is relevant to menus since menu widgets register mouse-button state on initialization, even when they don't have capture set. This means that menus created while the mouse button is down will set their state accordingly, but will not not register the mouse release event if they don't have focus. Fixing this is pre-req to support DnD on bookmark menus.

This is mitigated by updating the `is_mouse_button_pressed_` flag when setting capture, so that incoming mouse events will be handled appropriately (i.e., mouse-moved events won't be treated as drags).

Change-Id: I852a21078cb4f067948abfcd486bc87efe373eff
Bug: 40868588
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6092836
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Kaan Alsan <alsan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1397340}