pw_trace: Initial tokenized trace backend

Tokenized trace, implements trace events by tokenizing all compile time
information of the event into a 32bit number (using tokenizer module).

This CL just adds the encoding of trace events and callback hooks,
buffering which usies the callback will be added in a future CL.

Test: passes included test
Change-Id: Ibfcc34211c09965af8da030e28dba5e8f7c6ccdb
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/11428
Commit-Queue: Rob Oliver <rgoliver@google.com>
Reviewed-by: (☞゚∀゚)☞ Tennessee Carmel-Veilleux  <tennessee@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 8f098d7..8844c10 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -188,6 +188,7 @@
       "$dir_pw_string:tests",
       "$dir_pw_tokenizer:tests",
       "$dir_pw_trace:tests",
+      "$dir_pw_trace_tokenized:tests",
       "$dir_pw_unit_test:tests",
       "$dir_pw_varint:tests",
     ]