Add an option to inlineEditor to prevent the height-matching behavior.

In cases where we're rendering rich text formats like markdown, it's often that
the height of the raw text won't match the height of the rendered element.
Rather than try to do this matching and have it make the editor (often
significantly) too big, always autosize it to fit the source text.

By default, this will animate to the target size, which makes it seem just as
smooth as before. It's only if people have disabled animation that it will seem
jumpy.

Testing done:
Tested opening and closing the editor for various blocks of text. In
particular, I tested the empty case (animate to minimum size) and the case
where I had a big block of markdown text that rendered significantly larger
than the text (due to images). In all cases, the text box was sized
appropriately for the contents within, and the transitions were smooth.

Reviewed at https://reviews.reviewboard.org/r/4498/