I'll answer as an instrumentalist, since the question didn't specify only vocal performance. Vocalists definitely seem to focus on the effects of alcohol on their voice as well as on their mood and mind. Mostly I see them avoiding it—maybe avoiding it altogether, all the time, or at least in the immediate days before a performance. Others, especially in non-classical genres, might use alcohol on purpose to get a huskier voice.
But personally, the only performances that I can imagine drinking before would be ones that I wouldn't be nervous about anyway. For instance, if I was playing fiddle tunes in an Irish session or Old-time jam, I'm already there for fun and could imagine having a beer. But in most performance contexts, I need a lot of mental focus. If I'm playing a classical performance, in a solo role with all eyes on me, I need every brain cell I have to manage all the technical demands, remember the music itself, and remember all the interpretive nuances I've planned. Even if it's an orchestral concert where nobody will hear me in particular, I need to stay alert in the hard parts, and stay awake in the boring parts! Meanwhile, most of the non-classical playing I do involves improvisation, and I need a lot of brain power to know what the next "right note" is in time to play it, and to pick up on little things other band members are doing and respond to them.
But to your question about how widespread it is, there's certainly a lot of substance use around music-making. I get the impression that in the rock world it's standard practice to reach a certain level of buzz before taking the stage. And in the classical world, while I've very seldom seen anyone under the influence during a performance, there is certainly plenty of use in the "off hours." But I would say anecdotally that there's also a very high rate of dependance and abuse (of all sorts of substances) in the performing arts. Just because it's widespread doesn't mean it's a good idea in the long run, and I'm not sure it even helps anything in the short run.
Meanwhile, you might look into other ways of "hacking" your own mood. Many people take beta blockers to deal with strong performance anxiety. But if the goal is simply to "get yourself out of your shell," you might even find that a bit of cardio has a similar effect. Run a few laps around the green room and you'll get some blood flowing to your brain. Similarly, making sure you've eaten recently enough that you have a good blood sugar level can be important.