Move all test_constants to Jest

Also updates Karma to export * from them all

**Why?**

This helps with automatically migrating Karma specs to Jest

spec/frontend/helpers/test_constants.js

-// eslint-disable-next-line import/prefer-default-export
+export const FIXTURES_PATH = `/fixtures`;
 export const TEST_HOST = 'http://test.host';
+
+export const DUMMY_IMAGE_URL = `${FIXTURES_PATH}/static/images/one_white_pixel.png`;
+
+export const GREEN_BOX_IMAGE_URL = `${FIXTURES_PATH}/static/images/green_box.png`;
+export const RED_BOX_IMAGE_URL = `${FIXTURES_PATH}/static/images/red_box.png`;

spec/javascripts/test_constants.js

-export const FIXTURES_PATH = `/fixtures`;
-export const TEST_HOST = 'http://test.host';
-
-export const DUMMY_IMAGE_URL = `${FIXTURES_PATH}/static/images/one_white_pixel.png`;
-
-export const GREEN_BOX_IMAGE_URL = `${FIXTURES_PATH}/static/images/green_box.png`;
-export const RED_BOX_IMAGE_URL = `${FIXTURES_PATH}/static/images/red_box.png`;
+export * from '../frontend/helpers/test_constants';