Support for use of value from multi-valued LDAP attribute

Specific use-case:
Given a Microsoft-centric setup where users' email addresses are managed by Microsoft Exchange, which is tied into the same Active Directory instance Crowd is configured to synchronize from.

In this setup, users' email addresses are stored in a multi-valued LDAP attribute named proxyAddresses like so:

proxyAddresses: smtp:barbara@contoso.com
proxyAddresses: SMTP:Barbara.Sankovic@contoso.com
proxyAddresses: sip:barbara.sankovic@contoso.com
proxyAddresses: other:stuff

The primary email address which is usually (but not always and therein lies the issue) found in the mail attribute is stored as the entry in proxyAddresses that starts with SMTP: (note the colon).

This request is to add support to the core LDAP library in Crowd to support an expression to use during LDAP sync, something like ldap-multivalue-field[criteria] and get the specified value from the collection – for example proxyAddresses[SMTP:] which returns Barbara.Sankovic@contoso.com.