[trace][intelpt] Support system-wide tracing [11] - Read warnings and perf conversion in the client

- Add logging for when the live state of the process is refreshed
- Move error handling of the live state refreshing to Trace from TraceIntelPT. This allows refreshing to fail either at the plug-in level or at the base class level. The error is cached and it can be gotten every time RefreshLiveProcessState is invoked.
- Allow DoRefreshLiveProcessState to handle plugin-specific parameters.
- Add some encapsulation to prevent TraceIntelPT from accessing variables belonging to Trace.

Test done via logging:

```
(lldb) b main
Breakpoint 1: where = a.out`main + 20 at main.cpp:27:20, address = 0x00000000004023d9
(lldb) r
Process 2359706 launched: '/home/wallace/a.out' (x86_64)
Process 2359706 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x00000000004023d9 a.out`main at main.cpp:27:20
   24   };
   25
   26   int main() {
-> 27     std::vector<int> vvv;
   28     for (int i = 0; i < 100000; i++)
   29       vvv.push_back(i);
   30
(lldb) process trace start                                                                                        (lldb) log enable lldb target -F(lldb) n
Process 2359706 stopped
* thread #1, name = 'a.out', stop reason = step over
    frame #0: 0x00000000004023e8 a.out`main at main.cpp:28:12
   25
   26   int main() {
   27     std::vector<int> vvv;
-> 28     for (int i = 0; i < 100000; i++)
   29       vvv.push_back(i);
   30
   31     std::deque<int> dq1 = {1, 2, 3};
(lldb) thread trace dump instructions -c 2 -t                                                                     Trace.cpp:RefreshLiveProcessState                            Trace::RefreshLiveProcessState invoked
TraceIntelPT.cpp:DoRefreshLiveProcessState                   TraceIntelPT found tsc conversion information
thread #1: tid = 2359706
  a.out`std::vector<int, std::allocator<int>>::vector() + 26 at stl_vector.h:395:19
    54: [tsc=unavailable] 0x0000000000403a7c    retq
```

See the logging lines at the end of the dump. They indicate that refreshing happened and that perf conversion information was found.

Differential Revision: https://reviews.llvm.org/D125943