Hide keyboard while the home button get pressed

For multi-client IME, launcher need to call hideSoftInputFromWindow() by
using the InputMethodManager instance that mapped the presented display
while its home button get pressed.

Launcher 3 has already handled this part, but the secondary launcher
has not yet.

Bug: 120114697
Test: Manual verified that multi-client IME can be closed correctly.
Change-Id: I8959c3a470580452bfb95dbd4b4ce9268589000f