License style cleanup

[Rylan12]

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This PR does a few things:

1. License arrays are now converted to hashes in the license method rather than on-demand when needed by e.g. audit. This means that calling formula.license will always return either a string, symbol, or hash.
2. Deprecate license arrays. This will display a deprecation message whenever license [...] is called. This message would show up when running brew audit, brew install, etc.
3. brew style forbids using license arrays. brew style --fix will automatically correct license arrays to an :any_of hash.
4. brew style requires using multiple lines for license expressions if there are nested hashed. This means that license any_of: ["MIT", "0BSD"] is allowed but license any_of: ["MIT", "0BSD" => { with: "LLVM-exception" }] is not.

[MikeMcQuaid]

Great work as usual @Rylan12!

[scpeters]

If license arrays are no longer allowed, then I think bump-revision needs an update to revert 1ac470f from #8139, though I'm not sure if that will be sufficient to support symbols or hashes. I'll investigate further...

[Rylan12]

@scpeters I've got a fix in #8708