[asxxb]

Description

Fixes an issue where juce::Image::clear() is silently ignored on Direct2D-backed images when a juce::Graphics context is already active.

The existing implementation attempted to create another graphics context while the image was already being drawn to. Direct2D rejects the second context, leaving the active render target unchanged.

This change:

• Dispatches Image::clear() through ImagePixelData.
• Reuses the already-active Direct2D graphics context when available.
• Performs the clear using JUCE's existing rectangle-fill path with replacement/source semantics.
• Preserves the requested clear rectangle instead of clearing the entire render target.
• Adds a Direct2D regression test covering partial clears and pixels outside the cleared region.

Testing

• git diff --check — passed
• macOS CMake DemoRunner build — passed
• Direct2D/Windows runtime testing — not available in the current macOS environment; should be validated by Windows CI.