Preserve custom long-click listeners on navigation items

[sorinc03]

Summary

• avoid re-installing pre-O TooltipCompat long-click handling when a custom NavigationBarItemView long-click listener is present
• keep the existing L/M tooltip guard and platform tooltip behavior on O+
• add a Robolectric regression for a custom listener surviving a title refresh on API 24

Fixes #1368.

Test plan

• ./gradlew :lib:testDebugUnitTest --tests com.google.android.material.navigation.NavigationBarItemViewTest
• ./gradlew :lib:lintDebug
• git diff --check

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.