Add experimental session replay capturing on Linux

[tustanivsky]

This PR adds an opt-in session replay feature for Linux allowing the SDK to continuously record the last several seconds of gameplay into a MP4 file and attach it to crash reports.

Example crash event with Session Replay attached (Linux)

Key Changes

• The desktop recorder lifecycle (initialization, crash-time attachment, teardown, and replay path) is now consolidated into FGenericPlatformSentrySubsystem, the shared sentry-native base. All native desktop backends (Windows, Linux and the macOS Native backend) now use this unified path for Session Replay, and the duplicated implementations have been removed from FWindowsSentrySubsystem and the Native branch of FMacSentrySubsystem. The Cocoa backend retains its own implementation as it lives in a separate class hierarchy (FAppleSentrySubsystem).

• FSentryBackBufferCapture now selects the encoder input texture interop flag at runtime based on the active RHI type - External for Vulkan (Linux, or Windows with -vulkan) and Shared for D3D - aligning with how the engine’s FVideoResourceRHI::Create chooses the appropriate flag per RHI.

Engine Dependencies

In addition to AVCodecsCore, Linux builds require the experimental NVCodecs plugin (which provides the NVENC encoder, available on Win64/Linux from UE 5.2+). Both must be enabled in the project for USE_SENTRY_SESSION_REPLAY to be defined (guards session replay code), and the platform must be Win64, Mac, or Linux.

Other Considerations

• Vulkan → CUDA external-memory interop: On Linux the RHI is Vulkan, and AVCodecs has no native Vulkan H.264 encoder - NVENC is reached through CUDA. The encoder imports the capture texture's GPU allocation via an external-memory handle (OPAQUE_FD on Linux), which requires the texture to be created with TexCreate_External rather than the D3D-oriented TexCreate_Shared. The capture path now picks the flag per RHI so the Vulkan allocation exposes a shareable handle; with the wrong flag the resource has no shareable handle and the encoder rejects every frame.

Known Limitations

• Currently works only with NVIDIA GPUs (driver 530.41 or newer)

Documentation

• docs(unreal): Session Replay capturing on Linux sentry-docs#18366

Related items:

• Add experimental session replay capturing on Windows #1404
• Add experimental Session Replay capturing on Mac #1425

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[JoshuaMoelans]

nice consolidation work! (also cool that Linux is way less additional work than macOS 😁 )