[Dashboard] Simplify LogVirtualView

[alanwguo]

LogVirtualView component is very complex and utilizes react-window.

I think a simple component that just renders log lines directly into the DOM with the correct usage of memoization will have better performance and a better user behavior.

With react-window, log lines get re-rendered every time a user scrolls. This can be slow for large log files.

A browser can render many megabytes of text with no problem. But constantly re-rendering and re-layouting with scrolling can be very slow.

[anyscalesam]

@alanwguo beyond that first issue are there additional improvements?

[alanwguo]

Main benefits are:

1. Improved performance
2. Better support for copy-paste. Can copy-paste all the content instead of just the visible text.
3. simplify the code for easier maintenance.