WIP: Fix copying a single line from Firefox

What does this MR do?

This MR is related to converting pipeline logs to HTML (Ansi2HTML). The fix ensures that all open tags are closed before adding a
tag. As result: in Firefox, when selecting a line (with triple clicks) and copying, only one line will be copied.

The previous MR was reverted after merge because it had some issues: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/29832#note_184730332

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides

If cross-browser testing is not required, please remove the relevant item, or mark it as not needed: [-] -->

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

Closes #63406 (closed)