The mongos does not return WriteConcernError for findAndModify.

To reproduce: Setup a shard cluster of three nodes; create an unsharded or sharded collection and insert documents; stop one secondary replica from responding; send a findAndModifyCommand with writeConcern {w: 3, wtimeout: 1000}. The command response should include a WriteConcernError "WriteConcernTimeout".

This issue was discovered as part of the testing in SERVER-80103. Despite the fix for SERVER-97470, this test is still missing the WCE for sharded and unsharded collections.