message: Add BackstageTheme to core-components imports
diff: import { ApiRef } from '@backstage/core-plugin-api';
  import { BackstageIdentityApi } from '@backstage/core-plugin-api';
  +import { BackstageTheme } from '@backstage/theme';
  import { Breadcrumbs as Breadcrumbs_2 } from '@material-ui/core';
  import { ButtonProps } from '@material-ui/core';
  import { ButtonTypeMap } from '@material-ui/core';
  @@ -1604,6 +1605,13 @@ export const SidebarDivider: React_2.ComponentType<
  > &
  StyledComponentProps<'root'> & {
  className?: string | undefined;
  + } & Pick<
  + {
  + theme: BackstageTheme;
  + },
  + never
  + > & {
  + theme?: BackstageTheme | undefined;
  }
  >;
  