fix: duplicated xroutes are added to gatewayapi.Resources

[aoledk]

What type of PR is this?

Fix duplicated TLSRoute/HTTPRoute/GRPCRoute/TCPRoute/UDPRoute are added to gatewayapi.Resources when single xRoute is attaching to multiple Gateways.

What this PR does / why we need it:

When single xRoute is attaching to multiple Gateways, this case is normal, different listeners with distinct certificates or transport sockets should route traffic to same backend. Duplicated xRoutes will be processed in gatewayapi module, then listener's attachedRoutes will be incorrect.

Which issue(s) this PR fixes:

Fixes #3165