feat: add the pdf element

[tpatel]

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Description

• This element allows displaying local or remote pdf files in the chat UI
• For now the implementation is simple: the backend sends a base64 string to the frontend which creates a data-uri for an iframe
• Reworked the InlinedElements component to avoid looping multiple times over the elements array
• Simplified the types in element.ts
• Updated the view.tsx so that it takes advantage of TypeScript safety
• Updated the filenames for the components in components/element/inlined/ to show they support a collection of items

Screenshot

This feature uses the browser native PDF reader, hence the different pdf reader styles.

Firefox

Chrome

Safari