Add uid field annotation in atoms.proto and statd memory usage optimization.

[memory]
  statsd binary size from 664k -> 600k
  memory usage 1978k -> 1813k (with no configs)
  + Avoid initialize any static map in statslog.h to avoid many copies of the map in each include.
    - Do it in cpp so that it is initialized only in places that use them

[Uid annotation]
+ Uid annotation is needed for extracting uid from dimension for UidCpuPuller.
+ After the change, stand-alone uids don't need to be in field 1 anymore.
+ Also added exclusive bit annotation in AppDied
+ Currently only allow one uid field in an Atom. This is to keep things simple until
  we find an exception.

Test: statsd_test
Bug: 73958484
Bug: 72129300

Change-Id: I8a916d5c00d5930e24ae7e0825a57dea19c0e744
diff --git a/tools/stats_log_api_gen/Collation.h b/tools/stats_log_api_gen/Collation.h
index edba3e2..5d2c302 100644
--- a/tools/stats_log_api_gen/Collation.h
+++ b/tools/stats_log_api_gen/Collation.h
@@ -84,6 +84,8 @@
     vector<int> primaryFields;
     int exclusiveField = 0;
 
+    int uidField = 0;
+
     AtomDecl();
     AtomDecl(const AtomDecl& that);
     AtomDecl(int code, const string& name, const string& message);