As decided in https://gitlab.com/gitlab-org/gitlab-ce/issues/53593

reviewers.

Show masked switch for each variable
When toggled on, the variable value will be masked in runner logs
Show warning message if the switch is on but the value is not maskable

This reverts merge request !25476

Add a masked switch to variable rows
Copy some behavior from the protected switch

This reverts commit f5201a81, reversing
changes made to 48e6db0d.

This reverts merge request !25293

This adds a concern that abstracts the concept of masking a variable,
including the RegEx for validation.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/39118

Conflicts:
	app/views/ci/variables/_form.html.haml
	app/views/ci/variables/_table.html.haml
	ee/app/views/ci/variables/_environment_scope.html.haml
	spec/javascripts/ci_variable_list/ci_variable_list_ee_spec.js
	spec/javascripts/fixtures/projects.rb