Corrected terminology and added FCI (dotnet#5367)

See title. Fixed things that were not quite right as I've done with a lot of HA related stuff for SQL Server.

Author: allanhirt

xml/System.Data.SqlClient/SqlConnectionStringBuilder.xml

@@ -1818,7 +1818,7 @@ False
         <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>If your application is connecting to an AlwaysOn availability group (AG) on different subnets, setting MultiSubnetFailover=true provides faster detection of and connection to the (currently) active server. For more information about SqlClient support for Always On Availability Groups, see [SqlClient Support for High Availability, Disaster Recovery](/dotnet/framework/data/adonet/sql/sqlclient-support-for-high-availability-disaster-recovery).</summary>
+        <summary>If your application is connecting to an Always On availability group (AG) or Always On Failover Cluster Instance (FCI) on different subnets, setting MultiSubnetFailover=true provides faster detection of and connection to the (currently) active server. For more information about SqlClient support for the Always On features, see [SqlClient Support for High Availability, Disaster Recovery](/dotnet/framework/data/adonet/sql/sqlclient-support-for-high-availability-disaster-recovery).</summary>
         <value>Returns <see cref="T:System.Boolean" /> indicating the current value of the property.</value>
         <remarks>To be added.</remarks>
         <related type="Article" href="/dotnet/framework/data/adonet/ado-net-overview">ADO.NET Overview</related>