found_artifact() groundwork

Lay groundwork for generating a log event when finding an artifact
on the floor or carried by a monster.  This part should not produce
any change in behavior.

Move g.artidisco[] and g.artiexist[] out of the instance_globals
struct back to local within artifact.c.  They are both initialized
at the start of a game (and only used in that file) so don't need
to be part of any bulk reinitialization if restart-instead-of-exit
ever gets implemented.

Convert artiexist[] from an array of booleans to an array of structs
containing a pair of bitfields.  artiexist[].exists is a direct
replacement for the boolean; artiexist[].found is new but not put to
any significant use yet.  If will be used to suppress the future
found-an-artifact event for cases where a more specific event (like
crowning or divine gift as #offer reward) is already produced.

Remove g.via_naming altogether and add an extra argument to oname()
calls to replace it.

Add an extra argument to artifact_exists() calls.

include/hack.h

@@ -371,6 +371,11 @@ typedef struct sortloot_item Loot;
 #define BUCX_TYPES (BUC_ALLBKNOWN | BUC_UNKNOWN)
 #define ALL_TYPES_SELECTED -2
 
+/* Flags for oname() */
+#define ONAME_NO_FLAGS   0U /* none of the below */
+#define ONAME_VIA_NAMING 1U /* oname() is being called by do_oname() */
+#define ONAME_FOUND_ARTI 2U /* if an artifact, hero becomes aware of it */
+
 /* Flags to control find_mid() */
 #define FM_FMON 0x01    /* search the fmon chain */
 #define FM_MIGRATE 0x02 /* search the migrating monster chain */