Inject swipe events with fixed frequency

The current implementation of `input swipe` injects too many motion
events during the swipe simulation. This behavior is different from the
real situation and other tools such as UI Automator.
This CL adds a sleep between input events so that they are emitted with
fixed frequency (120Hz).

Bug: 373998306
Test: atest InputShellCommandTest
Test: adb shell input swipe 200 800 200 200
Test: adb shell input swipe 200 800 200 200 100
Flag: EXEMPT minor change with unit test
Change-Id: I8b0d1a387e910280da8676201797723c47567a3a