SourceLayout: Shuffle and collate the log result codes symbols

SourceLayout: Shuffle and collate the log result codes symbols

This collates all the small definitions spread around Squid for defining
and handling the TCP_* and UDP_* result code tags logged by Squid.

* log_type enumeration shuffled from enums.h
* log_type increment operator shuffled from client_db
* log_type strings shuffled from Format:: and built automatically
* is-HIT lookup test shuffled from ICP

Due to LogTags.cc being automatically built from the enum list we define
the shuffled functions as inline. This is not a problem due to their small
size. When the LogTags type is converted to a class thay can be de-inlined.