IW3 barrier clipping functionality

[regenerance]

Add bg_removeBarriers

Summary

This PR implements the bg_removeBarriers dvar.

When enabled, bg_removeBarriers modifies player collision behavior to allow clients to move through map barriers and player-clip volumes that would normally restrict movement.

The implementation is intended to provide consistent barrier removal functionality while preserving required movement behavior such as ladder interaction.

Dvar

bg_removeBarriers

Default: false

When enabled:

• Removes collision with player-clip barriers.
• Allows clients to access normally restricted areas of the map.
• Allows movement through invisible barriers and other player-blocking clip volumes.
• Preserves collision behavior required for normal player movement where necessary.
• Preserves ladder interaction.

When disabled, normal game collision behavior is used.

Implementation

The player movement collision mask is adjusted while bg_removeBarriers is enabled so that movement traces ignore the appropriate player-clip contents.

Special movement cases that depend on the original collision mask, such as ladder detection and interaction, retain the required collision behavior.

Scope

This change only affects player movement collision while bg_removeBarriers is enabled. The dvar is disabled by default and does not alter standard movement behavior unless explicitly enabled.

Testing

• Verified standard movement with the dvar disabled.
• Verified movement through player-clip barriers with the dvar enabled.
• Verified access to normally restricted map areas.
• Verified ladder detection and movement remain functional.
• Verified toggling the dvar restores the expected collision behavior.