feat: add alt text support for images

Author: yoo2001818

Diff for: packages/notion-types/src/block.ts

@@ -131,6 +131,7 @@ export interface BaseContentBlock extends BaseBlock {
   properties: {
     source: string[][]
     caption?: Decoration[]
+    alt_text?: Decoration[]
   }
   format?: {
     block_alignment: 'center' | 'left' | 'right'

Diff for: packages/react-notion-x/src/components/asset.tsx

@@ -280,8 +280,9 @@ export function Asset({
       source = block.properties?.source?.[0]?.[0]
     }
     const src = mapImageUrl(source, block as Block)
+    const altText = getTextContent(block.properties?.alt_text)
     const caption = getTextContent(block.properties?.caption)
-    const alt = caption || 'notion image'
+    const alt = altText || caption || 'notion image'
 
     content = (
       <LazyImage