Support bypassing TLS in the framework

This change comprises the following parts:

    [1] android.net.dns.ResolvUtil, containing methods that encapsulate the
        use of the high bit in netids used in DNS resolution contexts.

    [2] Updates to captive portal apps to call the ResolvUtil method that
        enables DNS-over-TLS bypass for the captive portal app process.

Test: as follows
    - builds
    - flashes
    - boots
    - runtest frameworks-net passes
Bug: 64133961
Bug: 72345192

Change-Id: I2072c1f68d6978fa0d7e9d8693135a2c51bb0f87