Log user timing metrics

What does this MR do?

When the performance bar is enabled (P+B key combo), we output metrics introduced by User Timing API into the console. At the moment of creating the MR the only view aware of these metrics is the snippet view.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

References #255613 (closed)