Fix trait codegen for timestamp member with timestampformat trait

[joewyz]

Current trait codegen implementation cannot generate correct fromNode() and createNode() for timestamp members because traits carried by the MemberShape are ignored by the generators. This PR fixes this by adding special handling for @timestampFormat trait.
For example, the following model:

@trait
structure StructMemberWithTimestampFormat {
    @timestampFormat("date-time")
    memberDateTime: Timestamp

    @timestampFormat("http-date")
    memberHttpDate: Timestamp

    memberEpochSeconds: MemberEpochSeconds

    memberList: TimeStampList

    memberMap: StringTimeStampMap
}

@timestampFormat("epoch-seconds")
timestamp MemberEpochSeconds

list TimeStampList {
    @timestampFormat("http-date")
    member: Timestamp
}

map StringTimeStampMap {
    key: String
    @timestampFormat("http-date")
    value:Timestamp
}

The generated fromNode() method after fix:

public static StructMemberWithTimestampFormatTrait fromNode(Node node) {
        Builder builder = builder().sourceLocation(node);
        node.expectObjectNode()
            .getMember("memberDateTime", n -> Instant.parse(n.expectStringNode().getValue()), builder::memberDateTime)
            .getMember("memberHttpDate", n -> Instant.from(DateTimeFormatter.RFC_1123_DATE_TIME.parse(n.expectStringNode().getValue())), builder::memberHttpDate)
            .getMember("memberEpochSeconds", n -> Instant.ofEpochSecond(n.expectNumberNode().getValue().longValue()), builder::memberEpochSeconds)
            .getArrayMember("memberList", n -> Instant.from(DateTimeFormatter.RFC_1123_DATE_TIME.parse(n.expectStringNode().getValue())), builder::memberList)
            .getObjectMember("memberMap", o -> {
                Map<String, Instant> value1 = new LinkedHashMap<>();
                Map<StringNode, Node> members1 = o.expectObjectNode().getMembers();
                for (Entry<StringNode, Node> entry1 : members1.entrySet()) {
                    Instant value2 = Instant.from(DateTimeFormatter.RFC_1123_DATE_TIME.parse(entry1.getValue().expectStringNode().getValue()));
                    String key2 = entry1.getKey().expectStringNode().getValue();
                    value1.put(key2, value2);
                }
                builder.memberMap(value1);
            });
        return builder.build();
}

The generated createNode(() method after fix:

@Override
protected Node createNode() {
        return Node.objectNodeBuilder()
            .sourceLocation(getSourceLocation())
            .withOptionalMember("memberDateTime", getMemberDateTime().map(m -> Node.from(m.toString())))
            .withOptionalMember("memberHttpDate", getMemberHttpDate().map(m -> Node.from(DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.ofInstant(m, ZoneOffset.UTC)))))
            .withOptionalMember("memberEpochSeconds", getMemberEpochSeconds().map(m -> Node.from(m.getEpochSecond())))
            .withOptionalMember("memberList", getMemberList().map(m -> {
                ArrayNode.Builder builder1 = ArrayNode.builder();
                for (Instant element2 : m) {
                    builder1.withValue(Node.from(DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.ofInstant(element2, ZoneOffset.UTC))));
                }
                return builder1.build();
            }))
            .withOptionalMember("memberMap", getMemberMap().map(m -> {
                ObjectNode.Builder builder1 = ObjectNode.builder();
                for (Entry<String, Instant> entry2 : m.entrySet()) {
                    StringNode key2 = Node.from(entry2.getKey());
                    builder1.withMember(key2, Node.from(DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.ofInstant(entry2.getValue(), ZoneOffset.UTC))));
                }
                return builder1.build();
            }))
            .build();
}

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