Add new ImsException to better handle ImsService errors

The ImsService can crash unexpectantly or not be available
for certain device configurations. Define a checked exception
ImsException to handle these cases instead of using
RuntimeExceptions.

Bug: 122480210
Test: atest FrameworksTelephonyTests
Change-Id: Ie3221d56a235c0e037d71e197f4972df31faa09b