This removes some legacy api deprecation notices in the console in
React 18.

- Replace the last this.context.router in projectSettings.es6 with
  this.props.router from withRouter HOC. (Tested this, works fine)

- Remove these, which are unused:

      SomeComponent.contextTypes = {
        router: PropTypes.object
      };

Doing this step in one commit, hoping it will make the diff easier to
review online.

e.g., not say 'duplicate import' for this code:

   import React from 'react'
   import type { ReactNode } from 'react'

…which used to work fine, but typescript-eslint's no-duplicate-imports
rule has been removed:

- typescript-eslint/typescript-eslint@47eeea9275bd
- https://typescript-eslint.io/rules/no-duplicate-imports/

We could do more with this plugin.

Only skimmed it, but some of the other features might require some
more config.

- https://github.com/import-js/eslint-plugin-import/blob/main/README.md#resolvers

(Meanwhile, I'll try not to think about how many dev dependencies
we bring in just for this cool rule.)

- Remove modifier='[object Object]' in generated bem elements
- Use the new React 18 root API in renderInBackbone

Update ESLint config to accept separate type imports in TS again