Resolve "Project slug does not auto populate in IE11"

What does this MR do?

Fixes an error on the 'New project' page when trying to replace whitespaces in the project name.

Replaces the RegExp constructor with literal notation for creating the regex as the constructor caused problems on IE 11 with the second argument being present.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/52686

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #52686 (closed)