pw_log: Add thread field to log.proto

- Updated unit tests to check for file and thread fields.

Change-Id: I644a772433a481690dba3515e87730484516a3aa
Requires: pigweed-internal:24040
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/85590
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Carlos Chinchilla <cachinchilla@google.com>
diff --git a/pw_system/log_backend.cc b/pw_system/log_backend.cc
index 4f127b9..e08ba2e 100644
--- a/pw_system/log_backend.cc
+++ b/pw_system/log_backend.cc
@@ -90,6 +90,7 @@
       log::EncodeLog(level,
                      flags,
                      module_name,
+                     /*thread_name=*/{},
                      file_name,
                      line_number,
                      timestamp,