logd: object layer format statistics

Simplify table generation by placing the line and header formatting
into each type's (UID, PID, TID) object. Switch to const return
values for the ownership passing functions (*ToName() functions
and methods). Use longer variable names to reduce confusion.

Switch from LINES To NUM for pruned column as that more accurately
reflects what is dropped since one entry can contain several lines.

Bug: 22855208
Change-Id: Ib110dce98a68cf5f844eb30f8a192a1f691eeba2