Always use Context.getSystemService() to get IMM in SysUI

This is a mechanical refactoring, which should have no observable
behavior difference at this moment.

We need this refactoring because InputMethodManager#getInstance() does
not work well on multi-display scenarios.

Bug: 115891476
Test: Manually made sure that IME still works on inline-reply
Change-Id: I266c17187c7faab4d436e19a4db7595cab4244ac