DSDA: Unhold other call on holding 1st call.

- When there is a performHold() on a call on 1 sub, try to unhold
all connections and conferences on the other sub.
- Effectively constitutes a 'swap' functionality, but from the telephony
layer instead of the Dialer layer.

Bug:240169164
Test: TelephonyConnectionTest
Live test on Pixel 7: receiving 2 calls on different subs.

Change-Id: I88912fd042daa3aff103133d67fac48d904e3993
3 files changed