These two are now doom/open-scratch-buffer. If you're in a project,
a (persistent) scratch buffer is opened. Otherwise, a non-persistent,
transient scratch buffer is opened.
If ARG (universal argument) is non-nil, then use the current window
instead of a new window (or popup, if feature/popup is enabled).
Also, the ex command :x[!] is improved. The BANG = open in current
window.