[Launcher3] Hide keyboard when fastscroller scrolling down and keyboard

shown

Implement keyboard hiding logic: Hide keyboard when scrolling down (y > mLastY) unless already requested (mRequestedHideKeyboard). Track hide request state to prevent redundant calls.

New added logic: Only hide keyobard while dragging the scrollbar

result video: https://photos.app.goo.gl/e4dYUUiUN3BujNUz9

Bug: 333967597
Flag: EXEMPT bugfix
Test: Manual
Change-Id: Id672763c69cbb37aeb7a1fd3f17eb168de9f49b4