Create environment variable for the project's own folder

Migrated issue

Reported by: jonathan1055

Related to !331 (merged)

Problem/Motivation

Many jobs now need to be run in the project's own folder which is named $CI_PROJECT_DIR/$_WEB_ROOT/modules/custom/$CI_PROJECT_NAME for modern Drupal, and $CI_PROJECT_DIR/$_WEB_ROOT/sites/all/modules/custom/$CI_PROJECT_NAME for the legacy Drupal 7 jobs.

It would be useful if we had an automatic variable for this path, so that it is easier for custom before_script and after_script rather than have to know how to assemble the path from these variables.

Proposed resolution

Create the variable in .create-environment-variables and write it to the build.env file so that it is available in every subsequent job

The new variable is named $DRUPAL_PROJECT_FOLDER

Remaining tasks

Test every job that uses the new variable:

D10

• composer-base, restoring composer.json.backup - checked here
• composer-lint - checked here
• phpstan - sed on the junit.xml artifact - checked here
• stylelint - checked here
• eslint - checked here
• cspell - checked here
• phpunit concurrent=0 - checked here
• test-only changes - checked here

D7

• composer-base, restoring composer.json.backup - checked here
• phpunit install-drupal with dependencies in .info not composer.json - checked here
• test-only changes - checked here