interval_ops shall stop using btequalimage (deduplication)

The btequalimage() header comment says:

 * Generic "equalimage" support function.
 *
 * B-Tree operator classes whose equality function could safely be replaced by
 * datum_image_eq() in all cases can use this as their "equalimage" support
 * function.

interval_ops, however, recognizes equal-but-distinguishable values:

  create temp table t (c interval);
  insert into t values ('1d'::interval), ('24h');
  table t;
  select distinct c from t;

The CREATE INDEX of the following test:

  begin;
  create table t (c interval);
  insert into t select x from generate_series(1,500), (values ('1 year 1 month'::interval), ('1 year 30 days')) t(x);
  select distinct c from t;
  create index ti on t (c);
  rollback;

Fails with:

  2498151 2023-10-10 05:06:46.177 GMT DEBUG:  building index "ti" on table "t" serially
  2498151 2023-10-10 05:06:46.178 GMT DEBUG:  index "ti" can safely use deduplication
  TRAP: failed Assert("!itup_key->allequalimage || keepnatts == _bt_keep_natts_fast(rel, lastleft, firstright)"), File: "nbtutils.c", Line: 2443, PID: 2498151

I've also caught btree posting lists where one TID refers to a '1d' heap
tuple, while another TID refers to a '24h' heap tuple.  amcheck complains.
Index-only scans can return the '1d' bits where the actual tuple had the '24h'
bits.  Are there other consequences to highlight in the release notes?  The
back-branch patch is larger, to fix things without initdb.  Hence, I'm
attaching patches for HEAD and for v16 (trivial to merge back from there).  I
glanced at the other opfamilies permitting deduplication, and they look okay:

[local] test=*# select amproc, amproclefttype = amprocrighttype as l_eq_r, array_agg(array[opfname, amproclefttype::regtype::text]) from pg_amproc join pg_opfamily f on amprocfamily = f.oid where amprocnum = 4 and opfmethod = 403 group by 1,2;
─[ RECORD 1 ]───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
amproc    │ btequalimage
l_eq_r    │ t
array_agg │ {{bit_ops,bit},{bool_ops,boolean},{bytea_ops,bytea},{char_ops,"\"char\""},{datetime_ops,date},{datetime_ops,"timestamp without time zone"},{datetime_ops,"timestamp with time zone"},{network_ops,inet},{integer_ops,smallint},{integer_ops,integer},{integer_ops,bigint},{interval_ops,interval},{macaddr_ops,macaddr},{oid_ops,oid},{oidvector_ops,oidvector},{time_ops,"time without time zone"},{timetz_ops,"time with time zone"},{varbit_ops,"bit varying"},{text_pattern_ops,text},{bpchar_pattern_ops,character},{money_ops,money},{tid_ops,tid},{uuid_ops,uuid},{pg_lsn_ops,pg_lsn},{macaddr8_ops,macaddr8},{enum_ops,anyenum},{xid8_ops,xid8}}
─[ RECORD 2 ]───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
amproc    │ btvarstrequalimage
l_eq_r    │ t
array_agg │ {{bpchar_ops,character},{text_ops,text},{text_ops,name}}

Thanks,
nm