Replace some \textit

[eisenwave]

Related to #2076

I'm not sure if it's worth dismantling all uses of \textit. There are ~150 left. This is just picking some low-hanging fruits in wording that might still be visited from time to time.

[tkoeppe]

Thanks! Could you have a look also in text.tex, that also contains three instances of "see \ref{...}" in a \textit.

[eisenwave]

I'll put it on my list of things to do once the repo is public and I can make updates to my PRs without things exploding.

[jensmaurer]

@eisenwave , the (technical) blockers are gone here, I think.