Half-Life: Alyx Updated for Steam Frame

This is a major update that adds support for Steam Frame standalone gameplay.

Optimizations for Steam Frame

• Made significant rendering and performance optimizations when running on Steam Frame, updating most of the engine without altering any of the content.
• Added foveated rendering support when running standalone on Steam Frame.
• Ported the game to ARM64/aarch64.
• Added support for depth reprojection when running on Steam Frame, allowing smooth gameplay at lower framerates.

General Fixes

• Additional performance improvements when running on desktop PCs.
• Removed 1 tick of latency on player hands and other simulated objects.
• Fixed some GPU configurations displaying a low-memory warning when they had plenty of memory available.
• Fixed cross-platform cloud saves on Linux.
• Fixed subtitles not appearing on Linux.
• Fixed the Main Menu flickering for some users.
• Fixed a bug where it was occasionally not possible to interact with items when starting a new game.