Track IME user requests explicitly

This adds a from_user property to the ImeRequestFinished atom, to allow
tracking IME requests that come directly as a result of user
interaction, as these are more important metrics-wise.

Test: android.view.inputmethod.cts.InputMethodStatsTest
Bug: 303041796
Change-Id: I93f6262912b3a28a3c32d819560fb54b7b1d9251