[Proposal] Give the Reagent examples some TLC

[mchughs]

I was going through some of the examples, in particular the react-context and the functional-components-and-hooks examples.

I noticed a lot of little issues.

Problems with both:

• Builds are based on lein-figwheel, a deprecated build tool. With examples you want to just start them up as quickly as possible to play around with the underlying example. You don't want to fiddle with a build. I'd propose using deps.edn and shadow-cljs as I believe they are more standard nowadays, but if there is a particular affinity for lein and figwheel we could atleast move it to figwheel-main.
• The versions for some of the dependencies are out-of-date which actually causes problems if you try to play around with new features in the example. I can bring everything up to date.
• Should explicitly pull in react and react-dom latest versions.

Just in react-context:

• No README.md present despite the index.html indicating there should be.
• It's pulling in [cljsjs/react-sortable-hoc "1.11.0-0"] as a depency ostensibly to just pull in react and react-dom?
• I think it makes sense to add a bit about react/useContext. This would require using the :>f tag too.

Just in functional-components-and-hooks:

• The build process is more complicated than it needs to be. Am I going to be going to prod with example code?
• The build compains it can't find react-dom if you don't include it as a dependency. (I don't see where it's being used though so it's kinda of weird. Any ideas?)

I'm happy to make an MR for these two and I can also take a look at the other ones as well. Is there anything I proposed which you disagree with?

[Deraen]

Sounds good.

Some of the examples are missing cljsjs react and react-dom dependencies as those were included in Reagent before 1.1.0.