Function calculate_bitmap_transform 

fn calculate_bitmap_transform(
    glyph: Glyph,
    pixmap: &Pixmap,
    draw_props: DrawProps,
    font_size: f32,
    upem: f32,
    bitmap_glyph: &BitmapGlyph<'_>,
    bitmaps: &BitmapStrikes<'_>,
) -> Affine

Calculate transform for bitmap glyphs.

This computes the final positioning transform for a bitmap glyph, taking into account:

• Glyph position within the run
• Bitmap scaling to match requested font size
• Bearing adjustments (outer and inner)
• Origin placement (top-left vs bottom-left)
• Special handling for Apple Color Emoji