[GPU] Fuse more eltwises for horizontally fused FC

[yeonbok]

Details:

• Target pattern: FCs to be fused by horizontal fusing pass and they have Add users which can be regarded as bias add. Here if we fuse the FCs as is, the fused pattern will be fused_fc -> VariadicSplit -> Add so the Adds cannot be fused to the FCs.
• This PR sets such Add users as the FC's bias inputs so that the fused FC can handle them as fused bias.

Tickets:

• CVS-151841