This also makes Script to return an array of commands instead of
concatented command, which is our current direction.

Currently the RegexpError can be raised when processing next stage which leads to 500 in different places of code base.
This adds early check that regexps used in only and except are valid.

This reverts commit 13e37a3e.

This is a temporary refactoring stub, that is planned to be removed
after removing legacy config processor.

As for now, we keep this class inside a oryginal config processor class.
We will move implementation to this class and delegate to it from
current config processor.

After original gitlab ci yaml processor not longer has relevant
impelemntation we will replace it with new configuration class.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Favor `unless` over `if` for negative conditions
(or control flow ||).

See #17478

Closes #17406