Input: add support for start and end decorations

[csillag]

(This PR is implemented on top of #100 and #101, so only the last few commits belong to this change.)

<Input
    placeholder="Search..."
    beforeStartDecoration={<SettingsIcon className="h-4 w-4 text-muted-foreground" />}
    startDecoration={<SettingsIcon className="h-4 w-4" />}
    endDecoration={<LaunchIcon className="h-4 w-4" />}
    afterEndDecoration={<LaunchIcon className="h-4 w-4 text-muted-foreground" />}
/>

Now gets us:

(We can adjust the exact style for the separator when we have agreement on the working of the code.)

This is required for the designs like this:

[github-actions]

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[lubej]

Rebase after #101