Fix overlap between operator name and heads-up notification

The title of heads-up notification was shown incompletely
because it's covered by operator name.
To fix this issue, the operator name should be hidden
when a heads-up notification is shown.

Fixes: b/116533819
Test: atest SystemUITests
Test: manual - enable config_showOperatorNameInStatusBar
               and show a heads-up notification

Change-Id: Id3318cd7cb2c9b6950392fadd11d02ab873d84c5