Use the RichText facets when copying post text (#2481)

* feat: serialize rich text to string

* feat: wire richTextToString to copy post text

src/lib/strings/rich-text-helpers.ts

@@ -0,0 +1,29 @@
+import {AppBskyRichtextFacet, RichText} from '@atproto/api'
+import {linkRequiresWarning} from './url-helpers'
+
+export function richTextToString(rt: RichText): string {
+  const {text, facets} = rt
+
+  if (!facets?.length) {
+    return text
+  }
+
+  let result = ''
+
+  for (const segment of rt.segments()) {
+    const link = segment.link
+
+    if (link && AppBskyRichtextFacet.validateLink(link).success) {
+      const href = link.uri
+      const text = segment.text
+
+      const requiresWarning = linkRequiresWarning(href, text)
+
+      result += !requiresWarning ? href : `[${text}](${href})`
+    } else {
+      result += segment.text
+    }
+  }
+
+  return result
+}