This PR fixes Metal Swing offscreen rendering behavior when the active
`GraphicsConfiguration` is not compatible with JBR shared textures, and
adds focused regression tests for the fallback path.
`AcceleratedSwingPainter` now explicitly falls back to software painting
for incompatible graphics configurations (for example,
offscreen/`BufferedImage` paint flows).

## Changes

- Introduced `SharedTexturesAdapter` as a small abstraction over JBR
shared textures so production code keeps using JBR while tests can
inject a fake adapter.
- Updated `MetalSwingRedrawer` to create and pass the shared texture
adapter into `AcceleratedSwingPainter`.
- Updated `AcceleratedSwingPainter` to support test injection and
preserve fallback behaviour for incompatible graphics configurations.
- Added minimal test hooks in `AcceleratedSwingPainter` with
`org.jetbrains.annotations.VisibleForTesting` so tests can validate
cache-reset behaviour.
- Added `org.jetbrains:annotations` as an `awtMain` dependency to use
`VisibleForTesting`. I can undo this and remove the annotation, but I
think it's worth keeping...
- Added `AcceleratedSwingPainterTest` covering:
  - fallback is used for incompatible `GraphicsConfiguration`
  - accelerated cache state is cleared on fallback
  - `dispose()` delegates to fallback painter

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Fixes https://youtrack.jetbrains.com/issue/SKIKO-1082

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Co-authored-by: Igor Demin <igordmn@users.noreply.github.com>