cli/named_args: better handle name conflicts in #to_paths

Before we used to evaluate all named arguments as local paths
first. This means that the following could be a name conflict.

$ brew edit src

If there was a local file or directory named src, it would default
to that. Otherwise it would search for a formula/cask with the
same name and return that.

Now it will only default to the local path if the named argument
starts or ends with a slash ('/') or includes a period ('.').
This means that in the event of a name clash with a normal package
name it will default to the package instead of the local file.

It also fixes an edge case where the following would be interpreted
as a tap name.

$ brew edit /src

Library/Homebrew/cli/named_args.rb

@@ -221,6 +221,10 @@ module Homebrew
         to_formulae_to_casks(only: only, method: :resolve)
       end
 
+      LOCAL_PATH_REGEX = %r{^/|[.]|/$}.freeze
+      TAP_NAME_REGEX = %r{^[^./]+/[^./]+$}.freeze
+      private_constant :LOCAL_PATH_REGEX, :TAP_NAME_REGEX
+
       # Keep existing paths and try to convert others to tap, formula or cask paths.
       # If a cask and formula with the same name exist, includes both their paths
       # unless `only` is specified.
@@ -230,9 +234,9 @@ module Homebrew
         @to_paths[only] ||= Homebrew.with_no_api_env_if_needed(@without_api) do
           downcased_unique_named.flat_map do |name|
             path = Pathname(name).expand_path
-            if only.nil? && File.exist?(name)
+            if only.nil? && name.match?(LOCAL_PATH_REGEX) && path.exist?
               path
-            elsif name.count("/") == 1 && !name.start_with?("./", "/")
+            elsif name.match?(TAP_NAME_REGEX)
               tap = Tap.fetch(name)
 
               if recurse_tap