Add @gitlab/web-ide use behind feature flag

app/assets/javascripts/ide/index.js

app/assets/javascripts/ide/init_gitlab_web_ide.js

app/controllers/ide_controller.rb

app/helpers/ide_helper.rb

config/feature_flags/development/vscode_web_ide.yml

config/webpack.config.js

ee/spec/features/ide/user_commits_changes_spec.rb

ee/spec/features/ide/user_opens_ide_spec.rb

package.json

spec/features/ide/user_commits_changes_spec.rb

spec/features/ide/user_opens_merge_request_spec.rb

spec/features/ide_spec.rb

...ojects/blobs/user_creates_new_blob_in_new_project_spec.rb

...sees_link_to_create_license_file_in_empty_project_spec.rb

spec/features/projects/files/user_edits_files_spec.rb

spec/features/projects/tree/create_directory_spec.rb

spec/features/projects/tree/create_file_spec.rb

spec/features/projects/tree/tree_show_spec.rb

spec/features/projects/tree/upload_file_spec.rb

spec/frontend/ide/init_gitlab_web_ide_spec.js