WIP: Cleanup HTML trace rendered by Ansi2html

What does this MR do?

As part of the cleanup after deploying collapsible job logs we needed to remove some extra <span> tags that were generated. This caused the overall size of the HTML to increase and potentially cause https://gitlab.com/gitlab-org/gitlab-ce/issues/63503

Although this may not fix yet the performance issue it contributes to having a cleaner HTML to work with.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Work still pending

• Use prepend-left-default to indent sub-sections
• Fix color resets: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30018#note_184956787
• reduce number of <span> tags by trying to include as much as possible inside a single tag. Right now we generate 1 <span> tag per line. Instead we should close/open tags when: (1) style changes, (2) start/end of a section, (3) to wrap the first line of a section (header), (4) to close the end of a trace.