[lldb-server] Reset stop reason of all threads when resuming

Summary:
This patch makes the stop reason reset logic similar to MacOS' debugserver, where exceptions are reset for all threads when resuming process for stepping or continuing (see MachThreadList::ProcessWillResume and MachThread::ThreadWillResume).

Resetting stop reasons on resume fixes problems where LLDB spuriously reports SIGTRAP signal stop reason for deleted breakpoints (both internal and public) and where LLDB stops on an internal breakpoint while stepping over while a breakpoint is hit in another thread. See PR45642 for details.

Reviewed By: jingham, labath

Differential Revision: https://reviews.llvm.org/D79308