Support Emergency calling in CTS

1) Move system dialer query code into DefaultDialerCache in
preparation to be able to override it for testing.
2) Implement test emergency phone account package name filter,
which restricts test emergency numbers to being dialed over
specific test connection services. For safety, real emergency
numbers will ignore this filter.

Bug: 138741228
Test: atest CtsTelecomTestCases; atest TelecomUnitTests
Change-Id: Iade1b4d704f86af0898c166c8f6369555cea9713