Update Drupal.gitignore with upstream conventions: prefix /web for drupal...

Update Drupal.gitignore with upstream conventions: prefix /web for drupal code; remove deprecated simpletest directory; allow project composer.json|lock at root; add /vendor, composer, robo, drush and drupal scripts to root

Drupal.gitignore

 # gitignore template for Drupal 8 projects
 #
 # earlier versions of Drupal are tracked in `community/PHP/`
+#
+# follows official upstream conventions:
+# https://www.drupal.org/docs/develop/using-composer
 
 # Ignore configuration files that may contain sensitive information
-/sites/*/*settings*.php
-/sites/*/*services*.yml
+/web/sites/*/*settings*.php
+/web/sites/*/*services*.yml
 
 # Ignore paths that may contain user-generated content
-/sites/*/files
-/sites/*/public
-/sites/*/private
-/sites/*/files-public
-/sites/*/files-private
+/web/sites/*/files
+/web/sites/*/public
+/web/sites/*/private
+/web/sites/*/files-public
+/web/sites/*/files-private
 
 # Ignore paths that may contain temporary files
-/sites/*/translations
-/sites/*/tmp
-/sites/*/cache
-
-# Ignore testing related files
-/sites/simpletest
+/web/sites/*/translations
+/web/sites/*/tmp
+/web/sites/*/cache
 
 # Ignore drupal core (if not versioning drupal sources)
-/core
+/web/vendor
+/web/core
+/web/modules/README.txt
+/web/profiles/README.txt
+/web/sites/development.services.yml
+/web/sites/example.settings.local.php
+/web/sites/example.sites.php
+/web/sites/README.txt
+/web/themes/README.txt
+/web/.csslintrc
+/web/.editorconfig
+/web/.eslintignore
+/web/.eslintrc.json
+/web/.gitattributes
+/web/.htaccess
+/web/.ht.router.php
+/web/autoload.php
+/web/composer.json
+/web/composer.lock
+/web/example.gitignore
+/web/index.php
+/web/INSTALL.txt
+/web/LICENSE.txt
+/web/README.txt
+/web/robots.txt
+/web/update.php
+/web/web.config
+
+# Ignore vendor dependencies and scripts
 /vendor
-/modules/README.txt
-/profiles/README.txt
-/themes/README.txt
-/sites/README.txt
-/sites/example.sites.php
-/sites/example.settings.local.php
-/sites/development.services.yml
-/.csslintrc
-/.editorconfig
-/.eslintignore
-/.eslintrc.json
-/.gitattributes
-/.ht.router.php
-/.htaccess
-/autoload.php
-/example.gitignore
-/index.php
-/INSTALL.txt
-/LICENSE.txt
-/README.txt
-/robots.txt
-/update.php
-/web.config
+/composer.phar
+/composer
+/robo.phar
+/robo
+/drush.phar
+/drush
+/drupal.phar
+/drupal