[TF] Move replay definitions from Base Source VPCs to Mod VPCs

[Bitl]

Description

When creating a TF2 mod with a copied and pasted client_ and server_ VPC file (which is the usual Source SDK workflow for mods prior to the TF2 SDK release), errors related to REPLAY_ENABLED are seen upon compilation. This is due to an $Include file in both client_base.vpc and server_base.vpc that is only allowed to be used in projects with the conditional $TF. Although this works for TF2, this doesn't work when trying to build other derived mods with this source code if you're using a copy-pasted VPC file. In addition, source_replay.vpc recommends that the file be placed in mod VPC files.

// If you are adding replay support to a specific game, you must include this
// file in both its client_* and server_*.vpc files.
//
// This file should not be included in client_base.vpc or server_base.vpc.

This PR aims to dismantle the source_replay implementation from the base source VPCs (client_base and server_base) into replay specific VPCs (server_replay_base.vpc and client_replay_base.vpc) that are included in the mod VPC (server_tf and client_tf). One respective file included into each TF VPC enables the REPLAY_ENABLED conditional. While this doesn't enable replay functionality for all mods (also according to source_replay.vpc), this an effective solution to fix the above listed issue.