Move file_get_content_headers() to a static method on a utility class

Problem/Motivation

We are cleaning up the file.module and file_get_content_headers() can be moved to a static utility class since it doesn't have any service dependencies.

Steps to reproduce

Proposed resolution

Move the contents of file_get_content_headers() to a static utility class and deprecate.

Remaining tasks

Update CR

User interface changes

N/A

Introduced terminology

N/A

API changes

Data model changes

N/A

Release notes snippet

N/A