Refactor Media Upload component

[pranvinit]

What?

Migrate the MediaUpload React component from a React Class to a Functional Component.

Why?

React introduced Hooks in version 16.8 and recommends defining components as functions instead of classes.

How?

Following this document

Testing Instructions

1. Open a post or page in the editor.
2. Insert a block that uses MediaUpload (e.g., the Image block).
3. Upload or select a new image.
4. Verify that the media picker appears, media is inserted successfully, and no errors occur.

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