feat: add array style flag for backward compatibility

[peternhale]

@W-12165862@

[mshanemc]

:QA notes:

using data:tree:import off of my sf-ified data branch, combined with files from https://github.com/mshanemc/cg1

flags is

files: arrayWithDeprecation({
      char: 'f',
      summary: messages.getMessage('flags.files'),
      exclusive: ['plan'],
      aliases: ['--sobjecttreefiles'],
      deprecateAliases: true,
    }),

✅ warning is produced and shows nicely.
👎🏻 message should match sf, which would say array-flag, not arrayFlag
💡 at this point in the code, you've already parsed the values and you know the flag name. We could output the real text they should have used. 😄

two values on the flag: ../bin/dev force:data:tree:import -f data/Account.json,data/Dealer__c.json
✅ worked (tree is freaky fast)

two values on two instances of the flag ../bin/dev force:data:tree:import -f data/Account.json,data/Dealer__c.json -f data/Motorcycle__c.json,data/Lead.json
✅ worked fine
👎🏻 warning is shown twice. Knowing what I know about the command, I'm not sure there's a good way to fix it, and I don't think this'll hit users much (you either use a comma-list, or the multi-flag thing, not both)