Use PreCall.start instead of context.startActivity when starting calls from call log.

For some reason not understood, startActivity with the call intent causes the current activity (MainActivity) to be paused, resumed, and paused again. This results in an opportunity to double-tap the row which causes the InCallUi to open in bubble mode (this is also not well understood).

In any event, PreCall.start eventually uses TelecomManager to place the call rather than startActivity, which is presumably the thing that fixes the problem.

Also refactored TestPreCallModule to remove the many test implementations of PreCall and remove the static field in the module which could cause test interference.

TEST=manual
Bug: 78187587
Test: manual
PiperOrigin-RevId: 193596093
Change-Id: I933020d33db1c158628f14b30c2681c59c86201b