tp: add docs generation to Python generated C++ tables

Add docs generation for Python based C++ tables and migrate the thread
and process tables to use it.

Change-Id: I30955618fbe9ec6217074fbde87484200aac935f
diff --git a/Android.bp b/Android.bp
index 345137e..000a6b4 100644
--- a/Android.bp
+++ b/Android.bp
@@ -9963,6 +9963,7 @@
     name: "perfetto_src_trace_processor_tables_tables_python_binary",
     srcs: [
         "python/generators/trace_processor_table/public.py",
+        "python/generators/trace_processor_table/util.py",
         "src/trace_processor/tables/android_tables.py",
         "src/trace_processor/tables/metadata_tables.py",
         "tools/gen_tp_table_headers.py",