Empty lines lost when cell is run

[isabela-pf]

When editing a markdown cell, I can add line breaks without text to add space between paragraphs as seen below.

When I run the cell, all empty lines disappear and the spacing becomes the default between paragraph spacing. Empty lines both before and after a line of text will disappear.

Users may want to manually space out paragraphs with empty lines, so we should figure out how to preserve empty lines in the final rendering of a cell.