Export page

Having a look at it.

I have a working export form. I rephrased the export options to be consistent and understandable since what we had in ldo was sometime surprising as an export result.

Remaining tasks are:

* Trying to cleanup the URI value expected to be an internal project ID in \Drupal\l10n_community\Controller\L10nCommunityLanguagesController::export().
* Doing additional testing with the ajax selector that have inconsistent behavior based on the step you follow to export (sometime the releases are not listed, sometime they generate an error). It's hard to define the blocking steps to reproduce.

I didn't open the merge request yet since the first remaining task is important to be cleanup in my opinion (but the commits are shared).

Two above points are fixed.

There is now the last step not working which is the project selection with autocomplete. I managed to extract the project ID from the autocomplete response but the AJAX process triggers the form submission despite not having clicked on "Export Gettext file".

I tried the tricks to use $form_state->setRebuild() in the ajax callback or the #limit_validation_errors attribute but it didn't change the outcome. When i input a project name in the field, the form is fully submitted and the triggering element is set to the full form (which is what we DONT want).

Once this issue is solved, the export form will be fully functional.

Trying to discuss with Thomas how to solve it.

Alright, the MR is now reviewable. Thank you TeeBeeCoder for the pair programming.

I allowed myself to rephrase the form input labels and comments to try to be more explicit for new comers.
I also added code context for the choices made in the MR.

Thanks for the hard work @Artusamak and @TeeBeeCoder!

Automatically closed - issue fixed for 2 weeks with no activity.