Rename libpq trace internal functions

Rename libpq trace internal functions

libpq's pqTraceOutputMessage() used to look like this:

    case 'Z':               /* Ready For Query */
        pqTraceOutputZ(conn->Pfdebug, message, &logCursor);
        break;

Commit f4b54e1ed98 introduced macros for protocol characters, so now
it looks like this:

    case PqMsg_ReadyForQuery:
        pqTraceOutputZ(conn->Pfdebug, message, &logCursor);
        break;

But this introduced a disconnect between the symbol in the switch case
and the function name to be called, so this made the manageability of
this file a bit worse.

This patch changes the function names to match, so now it looks like
this:

    case PqMsg_ReadyForQuery:
        pqTraceOutput_ReadyForQuery(conn->Pfdebug, message, &logCursor);
        break;

(This also improves the readability of the file in general, since some
function names like "pqTraceOutputt" were a little hard to read
accurately.)

Some protocol characters have different meanings to and from the
server.  The old code structure had a common function for both, for
example, pqTraceOutputD().  The new structure splits this up into
separate ones to match the protocol message name, like
pqTraceOutput_Describe() and pqTraceOutput_DataRow().

Reviewed-by: Yugo NAGATA <nagata@sraoss.co.jp>
Discussion: https://www.postgresql.org/message-id/flat/575e4f9d-acfe-45e3-b7f1-7e32c579090e%40eisentraut.org