Fix CategoryAxis labels not visible on Android XXHDPI devices

[Copilot]

Problem

Category X-axis labels were not visible on Android devices with XXHDPI screen density (density value of 3.0), while they displayed correctly on devices with lower density values.

Affected Devices

• ✅ Working: Pixel 7 (density 2.625), Redmi Note 11 Pro 5G (density 2.75)
• ❌ Broken: Samsung Galaxy A14 5G (density 3.0), OnePlus Nord CE4 lite (density 3.0)

Root Cause

The issue was in the Android-specific positioning logic in HorizontalLabelLayout.OnDraw() method in AxisLabelLayout.cs:

// Line 410-411: Forces actualSize height to DesiredHeight
actualSize = new SizeF(actualSize.Width, (float)DesiredHeight);

// Line 427: Uses DesiredHeight for positioning
float textY = ((float)yPos + MarginTop + (float)DesiredHeight / 2);

On XXHDPI devices, the DesiredHeight calculation was affected by density scaling, causing labels to be positioned outside the visible chart area.

Solution

Modified the positioning logic to use the original label height instead of the density-scaled DesiredHeight:

SizeF originalActualSize = actualSize; // Store original size
#if ANDROID
actualSize = new SizeF(actualSize.Width, (float)DesiredHeight);
#endif

// Use original height for consistent positioning across all densities
#if ANDROID
float textY = ((float)yPos + MarginTop + originalActualSize.Height / 2);
#else
float textY = yPos + MarginTop;
#endif

Impact

• ✅ Fixed: XXHDPI devices now show category axis labels correctly
• ✅ Preserved: No regression on lower density devices
• ✅ Consistent: Uniform positioning logic across all Android density values
• ✅ Platform-safe: Other platforms (iOS, Windows) unchanged

Testing

Validated positioning improvements:

• Density 2.625-2.75: Maintains existing behavior (0-1px difference)
• Density 3.0: Improved positioning by ~5px, bringing labels into visible area

Fixes #218.

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