Update translate code to use a redirection shim

[atuchin-m]

During secreview/slack discussion we decided to use current google translate scripts as is via a shim to redirect requests to brave backend.
The code/tests should be updated to use this approach.

[atuchin-m]

For QA: we also need to check here a migration from extension based translation: #23155

[stephendonner]

There's no test plan for this or #23155 - mind adding one @atuchin-m or @rebron ? Marking as QA/Blocked and QA/Test-Plan-Required in the interim. /cc @LaurenWags

[LaurenWags]

@rebron might be able to help with a test plan also

[atuchin-m]

@LaurenWags @stephendonner We have a test plan here for all things related to translate: https://docs.google.com/document/d/1hADNy20_UIXMe2vXFrTFfpB5NCGK6hBtNVXJBYIJLds/

Currently, I seems that currently we need to make do some sanity check (without the new flag).
After we need to do detailed checking using the plan.

@rebron can provide more details.

[LaurenWags]

thanks @atuchin-m

chatted with @rebron - he's going to grab the issue with the test plan for Google translate extension (there were a few iirc) so we can be sure we're checking the correct one.

[LaurenWags]

Labelling QA/Blocked pending additional information from @rebron