dev-cmd/typecheck: Tell the user how to configure Sorbet for taps

- The previous try of setting `--dir` to the tap path produced nonsense
  (as far as I could tell).
- So I added a `sorbet` directory to `homebrew/services` locally,
  with a copy of the main config file, and went back to the `tap_path.cd`
  approach.
- This is a bit better, as in more like I'd expect, but something in
  Sorbet's knowledge of the world still doesn't find the "core" classes
  like `Formula`, `Plist` in the case of
  `brew typecheck homebrew/services`.

```
lib/service/services_cli.rb:107: Unable to resolve constant Keg https://srb.help/5002
     107 |        elsif service.formula.opt_prefix.exist? && (keg = Keg.for service.formula.opt_prefix) && keg.plist_installed?
                                                                    ^^^

lib/service/services_cli.rb:216: Unable to resolve constant Plist https://srb.help/5002
     216 |          Plist.parse_xml(plist_data, marshal: false)
                    ^^^^^
```

Library/Homebrew/dev-cmd/typecheck.rb

@@ -44,16 +44,20 @@ class Typecheck < AbstractCommand
 
  sig { override.void }
  def run
- raise UsageError, "Cannot use --dir when specifying a tap." if args.named.present? && args.dir.present?
-
  update = args.update? || args.update_all?
+ tap_path = args.no_named? ? HOMEBREW_LIBRARY_PATH : args.named.to_paths(only: :tap).first
+ unless (tap_path/"sorbet").exist?
+ raise UsageError, "Sorbet typechecking is not supported for the #{args.named.first} tap. " \
+ "Add a `sorbet/` directory with a config file to the tap to enable it."
+ end
+
  groups = update ? Homebrew.valid_gem_groups : ["typecheck"]
  Homebrew.install_bundler_gems!(groups:)
 
  # Sorbet doesn't use bash privileged mode so we align EUID and UID here.
  Process::UID.change_privilege(Process.euid) if Process.euid != Process.uid
 
- HOMEBREW_LIBRARY_PATH.cd do
+ tap_path.cd do
  if update
  workers = args.debug? ? ["--workers=1"] : []
  safe_system "bundle", "exec", "tapioca", "dsl", *workers
@@ -97,11 +101,10 @@ def run
  end
 
  srb_exec += ["--ignore", args.ignore] if args.ignore.present?
- if args.file.present? || args.dir.present? || (tap_dir = args.named.to_paths(only: :tap).first).present?
+ if args.file.present? || args.dir.present?
  cd("sorbet") do
  srb_exec += ["--file", "../#{args.file}"] if args.file
  srb_exec += ["--dir", "../#{args.dir}"] if args.dir
- srb_exec += ["--dir", tap_dir.to_s] if tap_dir
  end
  end
  success = system(*srb_exec)