refactor(terminal): rewrite terminal virtualization

[ferothefox]

fixes various issues with the terminal, mainly:

• log heights in the terminal are now cached, so scrolling and using the scrollbar to drag should not cause jumping as we memoized the heights
• hints to the browser that this is a highly interactive element, so we should see less frame drops
• scroll to bottom button should now work more reliably as the value to scroll down is no longer hardcoded and uses the actual heights of the items
• other bug fixes and performance improvements