fix(form-builder): prevent Sanity UI autofocus behavior for image inp…

…ut dialog

This fixes an issue in Sanity UI that (wrongly) identifies the first text input as the first focusable element, and autofocuses it when the edit dialog is opened (In many cases the first focusable element inside the Dialog the hotspot/crop tool, and this should receive autofocus instead of the first text input)

packages/@sanity/form-builder/src/inputs/files/ImageInput/ImageInput.tsx

@@ -455,6 +455,7 @@ export default class ImageInput extends React.PureComponent<Props, ImageInputSta
         id={`${this._inputId}_dialog`}
         onClose={this.handleCloseDialog}
         width={1}
+        __unstable_autoFocus={false}
       >
         <PresenceOverlay>
           <Box padding={4}>