Deprecate _drupal_flush_css_js() and create a new AssetQueryString cache service

Problem/Motivation

Splitting off a child issue from #3014752: [PP-1] Convert drupal_rebuild(), drupal_flush_all_caches() and _drupal_flush_css_js() functions into cache Rebuilder class where @alexpott suggested in comment #83:

I think this issue could do with coming in 2 parts. One that deals with the new CSS / JS query string service and converting usages of _drupal_flush_css_js() and anything that accesses the 'system.css_js_query_string' state directly. And another that deals with drupal_flush_all_caches() and drupal_rebuild().

This issue is for the first part of that.

Steps to reproduce

Proposed resolution

• Deprecate _drupal_flush_css_js()
• Create a new AssetQueryString cache service
• Convert usages

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet