Move DTK_ISODOW DTK_DOW and DTK_DOY to be type UNITS rather than

RESERV. RESERV is meant for tokens like "now" and having them in that
category throws errors like these when used as an input date:

stark=# SELECT 'doy'::timestamptz;
ERROR:  unexpected dtype 33 while parsing timestamptz "doy"
LINE 1: SELECT 'doy'::timestamptz;
               ^
stark=# SELECT 'dow'::timestamptz;
ERROR:  unexpected dtype 32 while parsing timestamptz "dow"
LINE 1: SELECT 'dow'::timestamptz;
               ^

Found by LLVM's Libfuzzer

src/backend/utils/adt/datetime.c

@@ -103,8 +103,8 @@ static const datetkn datetktbl[] = {
 	{"d", UNITS, DTK_DAY},		/* "day of month" for ISO input */
 	{"dec", MONTH, 12},
 	{"december", MONTH, 12},
-	{"dow", RESERV, DTK_DOW},	/* day of week */
+	{"dow", UNITS, DTK_DOW},	/* day of week */
-	{"doy", RESERV, DTK_DOY},	/* day of year */
+	{"doy", UNITS, DTK_DOY},	/* day of year */
 	{"dst", DTZMOD, SECS_PER_HOUR},
 	{EPOCH, RESERV, DTK_EPOCH}, /* "epoch" reserved for system epoch time */
 	{"feb", MONTH, 2},
@@ -114,7 +114,7 @@ static const datetkn datetktbl[] = {
 	{"h", UNITS, DTK_HOUR},		/* "hour" */
 	{LATE, RESERV, DTK_LATE},	/* "infinity" reserved for "late time" */
 	{INVALID, RESERV, DTK_INVALID},		/* "invalid" reserved for bad time */
-	{"isodow", RESERV, DTK_ISODOW},		/* ISO day of week, Sunday == 7 */
+	{"isodow", UNITS, DTK_ISODOW},		/* ISO day of week, Sunday == 7 */
 	{"isoyear", UNITS, DTK_ISOYEAR},	/* year in terms of the ISO week date */
 	{"j", UNITS, DTK_JULIAN},
 	{"jan", MONTH, 1},

src/backend/utils/adt/timestamp.c

@@ -4458,6 +4458,26 @@ timestamp_part(PG_FUNCTION_ARGS)
 				result = date2isoyear(tm->tm_year, tm->tm_mon, tm->tm_mday);
 				break;
 
+			case DTK_DOW:
+			case DTK_ISODOW:
+				if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+							 errmsg("timestamp out of range")));
+				result = j2day(date2j(tm->tm_year, tm->tm_mon, tm->tm_mday));
+				if (val == DTK_ISODOW && result == 0)
+					result = 7;
+				break;
+
+			case DTK_DOY:
+				if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+							 errmsg("timestamp out of range")));
+				result = (date2j(tm->tm_year, tm->tm_mon, tm->tm_mday)
+						  - date2j(tm->tm_year, 1, 1) + 1);
+				break;
+
 			case DTK_TZ:
 			case DTK_TZ_MINUTE:
 			case DTK_TZ_HOUR:
@@ -4481,26 +4501,6 @@ timestamp_part(PG_FUNCTION_ARGS)
 #endif
 				break;
 
-			case DTK_DOW:
-			case DTK_ISODOW:
-				if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
-					ereport(ERROR,
-							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-							 errmsg("timestamp out of range")));
-				result = j2day(date2j(tm->tm_year, tm->tm_mon, tm->tm_mday));
-				if (val == DTK_ISODOW && result == 0)
-					result = 7;
-				break;
-
-			case DTK_DOY:
-				if (timestamp2tm(timestamp, NULL, tm, &fsec, NULL, NULL) != 0)
-					ereport(ERROR,
-							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-							 errmsg("timestamp out of range")));
-				result = (date2j(tm->tm_year, tm->tm_mon, tm->tm_mday)
-						  - date2j(tm->tm_year, 1, 1) + 1);
-				break;
-
 			default:
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -4672,6 +4672,26 @@ timestamptz_part(PG_FUNCTION_ARGS)
 				result = date2isoyear(tm->tm_year, tm->tm_mon, tm->tm_mday);
 				break;
 
+			case DTK_DOW:
+			case DTK_ISODOW:
+				if (timestamp2tm(timestamp, &tz, tm, &fsec, NULL, NULL) != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+							 errmsg("timestamp out of range")));
+				result = j2day(date2j(tm->tm_year, tm->tm_mon, tm->tm_mday));
+				if (val == DTK_ISODOW && result == 0)
+					result = 7;
+				break;
+
+			case DTK_DOY:
+				if (timestamp2tm(timestamp, &tz, tm, &fsec, NULL, NULL) != 0)
+					ereport(ERROR,
+							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+							 errmsg("timestamp out of range")));
+				result = (date2j(tm->tm_year, tm->tm_mon, tm->tm_mday)
+						  - date2j(tm->tm_year, 1, 1) + 1);
+				break;
+
 			default:
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -4693,26 +4713,6 @@ timestamptz_part(PG_FUNCTION_ARGS)
 #endif
 				break;
 
-			case DTK_DOW:
-			case DTK_ISODOW:
-				if (timestamp2tm(timestamp, &tz, tm, &fsec, NULL, NULL) != 0)
-					ereport(ERROR,
-							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-							 errmsg("timestamp out of range")));
-				result = j2day(date2j(tm->tm_year, tm->tm_mon, tm->tm_mday));
-				if (val == DTK_ISODOW && result == 0)
-					result = 7;
-				break;
-
-			case DTK_DOY:
-				if (timestamp2tm(timestamp, &tz, tm, &fsec, NULL, NULL) != 0)
-					ereport(ERROR,
-							(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
-							 errmsg("timestamp out of range")));
-				result = (date2j(tm->tm_year, tm->tm_mon, tm->tm_mday)
-						  - date2j(tm->tm_year, 1, 1) + 1);
-				break;
-
 			default:
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),