Enhance the preview mode to support search result/link highlighting in line-level granularity

Edit: @GLight Thank you for merging this with my related request / bug report.

To developers: when implementing this, please make sure to unfold the quotation of my report in the post above, or look directly at OnClick on search result: Scroll to matched text also in Preview mode. It shows issue of the matched text actually being scrolled out of view, which is exactly opposite of the intent to move it into view and highlight. That deserves fixing (after higher priorities). Thanks