[offload][L0][NFC] Rename L0ContextTy to L0DriverTy (#236105)
The L0 plugin currently has two similarly named classes that serve
completely different purposes:
- `L0ContextTy`, which is misleadingly named as it holds per-driver
state,
- `LevelZeroPluginContextTy` which implements `PluginContextTy` and
actually owns an L0 context and related per-context state.
Rename `L0ContextTy` to `L0DriverTy`, and the containing source files to
L0Driver.h and L0Driver.cpp. Rename members and accessors accordingly
(e.g. `getL0Driver()`, `DriverList`).
Assisted-by: Claude Opus 5.5
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>