vhost-device-gpu: Refactor vhost-device-gpu

This commit refactors vhost-device-gpu by separating
virglrenderer from rutabaga, and using gfxstream via
rutabaga, Simplifying future backend development.

This commit introduces a significant refactor of the
virtio-gpu backend architecture:
- Transition `gfxstream` support to use `Rutabaga`
  abstraction.
- Decouple `virglrenderer` from `Rutabaga`, allowing
  it to be used as standalone.
- Unify backend handling using thread-local storage
  and macro-based runtime dispatch.

Key Changes:
VirglRenderer Backend:
   - `virgl.rs` is now a standalone backend that
     directly calls `libvirglrenderer` functions.
   - Removed reliance on `rutabaga` for virgl path.

Gfxstream Backend via Rutabaga:
   - Introduced `gfxstream.rs` backend using `rutabaga`
   - Thread-local `GfxstreamAdapter` manages its own
     `Rutabaga` instance, initialized lazily.
   - Preserved internal `GfxstreamResource` tracking
     with scanout support and memory handling.

Renderer Selection Logic:
   - In `device.rs`, `lazy_init_and_handle_event()` now:
     - Dispatches `VirglRendererAdapter` and
       `GfxstreamAdapter` using thread-local storage(TLS)
   - Introduced `extract_backend_and_vring()` helper for
     reusing backend setup logic.

Code Deduplication:
   - Abstracted common logic for both backends to common.rs.
   - Shared helpers reused between gfxstream and virgl.
   - Improved modularity with fewer duplicated error
     handling branches.

Testing and Validation:
   - Replaced `virtio_gpu.rs` testing paths with new unit
     tests for `gfxstream.rs` and `virgl.rs`.
   - Added code coverage for the new refactored crate.
   - Update coverage file to reflect the drop in coverage
     due to exclusion of some gfxstream tests from CI
     since they can't run in CI without GPU drivers.

Signed-off-by: Dorinda Bassey <[email protected]>

Author: Dorinda Bassey

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 86.60,
+  "coverage_score": 85.19,
   "exclude_path": "xtask",
   "crate_features": ""
 }

vhost-device-gpu/CHANGELOG.md

@@ -5,6 +5,8 @@
 
 ### Changed
 
+- [[#852]] (https://github.com/rust-vmm/vhost-device/pull/890) vhost-device-gpu: Refactor vhost-device-gpu
+
 ### Fixed
 
 ### Deprecated