Improve rendering performance when a file contains millions of characters

[Rob--W]

The viewer becomes unresponsive for a few seconds (or even more) when a really large file is opened. When the file contains any unicode characters, the rendering time is even quadrupled.

This is not specific to the extension, it also happens in a blank document and other browsers such as Firefox.

I should try to develop a partial view, which renders only the visible lines.