Add a test for parsing a packet with many compressed questions.

In order to do this, write some simple DNS compression code and
a test for it. The reason for adding the code here is:

- It's not easy for this code to depend on the production
  implementation because it's in a different respository.
- It's generally a good thing for test code not to depend on
  production code too much.

Bug: 263429226
Test: test-only change
Change-Id: Ice1380d2f1b2d568fe51580e014071089593f67d
1 file changed