HtmlConversion: Add support for telephone links (#2365)

Summary:
- This will allow html anchor tags with "tel:" prefixed hrefs to be rendered as links using the convertFromHTML method

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**Summary**

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**Test Plan**

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Pull Request resolved: #2365

Reviewed By: creedarky

Differential Revision: D21318447

Pulled By: mrkev

fbshipit-source-id: d352eb7c731724dfe80e6c86a882f7b59ac88520

src/model/encoding/convertFromHTMLToContentBlocks.js

@@ -154,7 +154,8 @@ const isValidAnchor = (node: Node) => {
     anchorNode.href &&
     (anchorNode.protocol === 'http:' ||
       anchorNode.protocol === 'https:' ||
-      anchorNode.protocol === 'mailto:')
+      anchorNode.protocol === 'mailto:' ||
+      anchorNode.protocol === 'tel:')
   );
 };