Markdown Preview auto-scrolling to the top when text is edited

[mlg556]

Description

I do not know if this can be called a "bug", but every time the markdown file is edited and the Markdown Preview window refreshes, the preview is scrolled to the very top each time. It really becomes annoying when you are in the process of writing and the preview suddenly jumps to the top you have to scroll it back down again to where you are.

Reproduce

Open and edit a long enough markdown file with Markdown Preview on.

Expected behavior

It shouldn't really scroll all the way to the top.

Context

• Operating System and version: macOS Mojave 10.14.4
• Browser and version: Safari 12.1
• JupyterLab version: 1.1.4

[jasongrout]

These issues are related: #8370 #9900 #4323