Add support for parsing time zones in DateFormatters and enhance Iso8601Parser

We can now parse ISO date-time such as :

2029-05-15T17:14:56.123456789-08:00[America/Los_Angeles]

or

2031-12-03T10:15:30.123456789+01:00:00[Europe/Paris]

Author: jycr

server/src/main/java/org/elasticsearch/common/time/Iso8601Parser.java

@@ -477,6 +477,10 @@ private ZoneId parseZoneId(CharSequence str, int pos) {
         if (minutes == null || minutes > 59) return null;
         if (len == pos) return ofHoursMinutesSeconds(hours, minutes, 0, positive);
 
+        if (str.charAt(pos) == '[' && str.charAt(len - 1) == ']') {
+            return parseRawZoneId(str, pos);
+        }
+
         // either both dividers have a colon, or neither do
         if ((str.charAt(pos) == ':') != hasColon) return null;
         if (hasColon) {
@@ -487,10 +491,29 @@ private ZoneId parseZoneId(CharSequence str, int pos) {
         if (seconds == null || seconds > 59) return null;
         if (len == pos) return ofHoursMinutesSeconds(hours, minutes, seconds, positive);
 
+        if (str.charAt(pos) == '[' && str.charAt(len - 1) == ']') {
+            return parseRawZoneId(str, pos);
+        }
+
         // there's some text left over...
         return null;
     }
 
+    /**
+     * Parses a raw zone id, which is a string of the form [zoneId] (eg [Europe/Paris]).
+     *
+     * @param str The string to parse
+     * @param pos The position in the string where the zone id starts (the first character after the opening [)
+     * @return The parsed zone id, or {@code null} if the string is not a valid zone id.
+     */
+    private ZoneId parseRawZoneId(CharSequence str, int pos) {
+        try {
+            return ZoneId.of(str.subSequence(pos + 1, str.length() - 1).toString());
+        } catch (DateTimeException e) {
+            return null;
+        }
+    }
+
     /*
      * ZoneOffset.ofTotalSeconds has a ConcurrentHashMap cache of offsets. This is fine,
      * but it does mean there's an expensive map lookup every time we call ofTotalSeconds.

server/src/test/java/org/elasticsearch/common/time/DateFormattersTests.java

@@ -608,6 +608,13 @@ public void testIso8601Parsing() {
         formatter.format(formatter.parse("2018-05-15T17:14:56,123456789+01:00"));
     }
 
+    public void testParsingDateTimeWithZoneId() {
+        DateFormatter formatter = DateFormatters.forPattern("strict_date_optional_time");
+        formatter.format(formatter.parse("2018-05-15T17:14:56-08:00[America/Los_Angeles]"));
+        formatter.format(formatter.parse("2029-05-15T17:14:56.123456789-08:00[America/Los_Angeles]"));
+        formatter.format(formatter.parse("2031-12-03T10:15:30.123456789+01:00:00[Europe/Paris]"));
+    }
+
     public void testRoundupFormatterWithEpochDates() {
         assertRoundupFormatter("epoch_millis", "1234567890", 1234567890L);
         // also check nanos of the epoch_millis formatter if it is rounded up to the nano second