sql: add cast support to TimeTZ

Added the various casts supported by postgres for `timetz`:

```
otan=# select
  castcontext,
  f.typname as "from",
  t.typname as to
from pg_cast
join pg_type as f ON (f.typelem = castsource)
join pg_type as t on (t.typelem=casttarget)
where
  castsource = 'timetz'::regtype or
  casttarget = 'timetz'::regtype;
 castcontext |     from     |   to
-------------+--------------+---------
 i           | _time        | _timetz
 a           | _timestamptz | _timetz
 i           | _timetz      | _timetz
 a           | _timetz      | _time
(4 rows)
```

No release not required as this will be combined with a fully fleshed
note for TimeTZ.

Release note: None

pkg/sql/logictest/testdata/logic_test/timetz

@@ -46,3 +46,29 @@ query TTI
 SELECT a::string, b::string, c FROM timetz_test WHERE a = b ORDER BY c
 ----
 15:00:00+03:00:00  15:00:00+03:00:00  5
+
+# Test various casts involving different timezones.
+subtest cast_tests
+
+statement ok
+SET TIME ZONE -5
+
+query T
+SELECT '11:00+03:00'::timetz::time
+----
+0000-01-01 11:00:00 +0000 UTC
+
+# This should take the timezone in the background.
+query T
+SELECT '11:00'::time::timetz
+----
+0000-01-01 11:00:00 -0500 -0500
+
+# This should observe the time and zone from the timestamp.
+query T
+SELECT '2001-01-01 11:00+04:00'::timestamptz::timetz
+----
+0000-01-01 11:00:00 +0400 +0400
+
+statement ok
+SET TIME ZONE UTC

pkg/sql/sem/tree/eval.go

@@ -3442,6 +3442,8 @@ func PerformCast(ctx *EvalContext, d Datum, t *types.T) (Datum, error) {
 			return ParseDTime(ctx, d.Contents)
 		case *DTime:
 			return d, nil
+		case *DTimeTZ:
+			return MakeDTime(d.TimeOfDay), nil
 		case *DTimestamp:
 			return MakeDTime(timeofday.FromTime(d.Time)), nil
 		case *DTimestampTZ:
@@ -3457,7 +3459,12 @@ func PerformCast(ctx *EvalContext, d Datum, t *types.T) (Datum, error) {
 			return ParseDTimeTZ(ctx, string(*d))
 		case *DCollatedString:
 			return ParseDTimeTZ(ctx, d.Contents)
-			// TODO(otan#26097): expand for other valid types.
+		case *DTime:
+			return NewDTimeTZFromLocation(timeofday.TimeOfDay(*d), ctx.GetLocation()), nil
+		case *DTimeTZ:
+			return d, nil
+		case *DTimestampTZ:
+			return NewDTimeTZFromTime(d.Time), nil
 		}
 
 	case types.TimestampFamily: