LPS-52270 Date_sortable FieldName should be saved as long type in solr

**The issue was caused by we saved date value as String type in solr so that when we search by date and it will order by String**. For example:

When we create three different web content articles and their publishDate are as the followings.

A:2000-01-01 (epoch value: 946734540000)
B:2001-01-01 (epoch value: 978357120000)
C:2014-01-01 (epoch value: 1388584380000)

In Asset Publisher portlet, if we choose "order by publishDate desc", the order will be B-A-C. In LPS-42802 commit "The value of numeric field should be the time in milliseconds", we will convert date to milliseconds as numeric(long) to save in solr. Please see DocumentImpl.addDate() method.

Due to we didn't define detailed dateField(for example: publishDate_sortable) in schema.xml, it will map with the field <dynamicField indexed="true" multiValued="true" name="*_sortable" stored="true" type="string" />. On this "name="*_sortable"" field, its store type is String so that Date field used String order.

In Asset Publisher Portlet, we can use "expirationDate,createDate,modified and publishDate" to order and the program will add "_sortable" as suffix to compose query sort. Please refer to AssetUtil.getSortType(String sortField) and BaseIndexer.getSortField(String orderByCol, int sortType) method. So the query sort will be "sort=expirationDate_sortable+asc".

The fix add four field so that Date field will be order by Long type. Through refer to the below link:
http://wiki.apache.org/solr/SchemaXml
**Using <dynamicField> declarations, you can create field rules that Solr will use to understand what datatype should be used whenever it is given a field name that is not explicitly defined, but matches a prefix or suffix used in a dynamicField.**

It means if we give a field name explicitly, it won't match with <dynamicField>. That is to say, <field> will firstly be matched. And then map with <dynamicField> if <field> doesn't be matched.

Please help check it.

Thanks,
Hai