Set language cookie domain to allow for cross-domain cookies

[chrisgarrity]

Resolves:

Part of fixing #3325

Changes:

Add leading . to the current hostname for the language cookie domain.

The scratchlanguage cookie was being set as scratch.mit.edu rather than .scratch.mit.edu, note the leading . Other backend servers processing the project creation did not have access to the cookie.

Test Coverage:

Manual testing prerequisites:

• access to the database where project metadata is stored
• open dev tools and delete the scratchlanguage cookie

• default language setting in the browser is used if cookie is not set
  • open browser settings and add another language, place it first in the language list
  • click create
  • editor loads in the new default language, and the project in the database has the same language in metadata

Delete the cookie in between these tests:

• scratchlanguage cookie is used if set on www
  • On a www page (e.g., home, explore...), choose a language in the language menu
  • create a project
  • editor loads in the new language, and project in the database also has the same language
  • in devtools...Application...Cookies, the domain for the scratchlanguage cookie starts with .
• scratchlanguage cookie is used if set on scratchr2
  • On a scratchr2 page (e.g., profile, studios), choose a language in the language menu
  • create a project
  • editor loads in the new language, and project in the database also has the same language
  • in devtools...Application...Cookies, the domain for the scratchlanguage cookie starts with .
• scratchlanguage cookie is used if set in the editor
  • In the editor, change language
  • use File...New to create a new project
  • editor loads in the new language, and project in the database also has the same language
• in devtools...Application...Cookies, the domain for the scratchlanguage cookie starts with .

[chrisgarrity]

This seems like a candidate for not testing on all browsers since it's mostly back-end. Then again, do we trust cookies to work the same on every browser? /cc @BryceLTaylor

[rschamp]

I think we probably should test on several browsers once this is on scratch.ly, but we probably don't need to bring it to the bug hunt for everyone to look at.