chore(storage-browser): Rename base class to mitigate block confusion

[cshfang]

Description of changes

This PR updates the AMPLIFY_CLASS_BASE constant to be named as STORAGE_BROWSER_BLOCK in an attempt to mitigate ongoing confusion about what a block is in the class names throughout the components.

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Latest commit: e86e6001af52f882b43d65bd31da0ca8b3305133

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