Research other setup-* repos to see what they cover

[PoshAlpaca]

Results of research looking at setup-* GH actions for Node, Python, Java and Go:

• Their *-version parameter usually supports SemVer version range syntax and is usually optional (except for Java)
• They make use of caching by using the runner's tools cache when possible (e.g. Python & Java) and caching downloaded versions (e.g. Node & Go)
• They all support caching of package manager dependencies (off by default), configured via the cache key, by using actions/cache internally
• Node and Java support publishing to package registries
• All of them register problem matchers for error output

[sergeysova]

It would be very cool if I can cache the downloaded swift version between the runs.