[TF2] Add client ConVars for changing viewmodel position and angle offsets

[Bradasparky]

Description

Currently, the only option for modifying your viewmodel offset is tf_use_min_viewmodels, which is a hard coded z value. This PR allows players to modify their viewmodel offsets however they want.

Added ConVars
- viewmodel_offset_x
- viewmodel_offset_y
- viewmodel_offset_z
- viewmodel_offset_pitch
- viewmodel_offset_yaw
- viewmodel_offset_roll

Notes

• Modified tf_viewmodels_offset_override to include angle arguments.
• When tf_use_min_viewmodels 1 is used with a non-zero value of viewmodel_offset_z, both offsets will be added together.
• Works with +inspect and weapon lowering during the game over round state or when in TF_COND_PHASE.

viewmodel.offset.showcase.mp4

[copperpixel]

IMO it would be better to do this in baseviewmodel_shared and apply it to other games similarly to Valve's implementation in Alien Swarm

[Bradasparky]

IMO it would be better to do this in baseviewmodel_shared and apply it to other games similarly to Valve's implementation in Alien Swarm

I'll look into doing that. I see that the Alien Swarm SDK's baseviewmodel_shared.cpp has the same positional offset convars.