[lldb] Improve logging for process state change (NFC)

This patch improves process state change logging messages to include to
process plugin name.

It also replaces the `LLDB_LOGF` macro by `LLDB_LOG` macro that adds the
class and method name in the log message using the compiler instead of
having to change the string litteral for every method.

This is very useful when investigating interactions between different
types of process plugins. That comes very handy when investigating bugs
related to interactive scripted process debugging.

Differential Revision: https://reviews.llvm.org/D148399



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>