Maintain stable shell layouts

[yugangw-msft]

The help/sample panel at the bottom automatically bumps up the cursor's position for a few lines while i am still in the typing. The appears quirky and surprises me a bit.
Suggest offer an option so people can at least reserve an estate for samples, and therefore maintains the layouts

Repro:
In shell, type the az vm create command close to the screen's bottom, a second later samples shows up in the bottom and my cursor gets moved up automatically.