feat(tap-info): display Git information about non-Core/non-API taps

Copy and tweak code from Library/Homebrew/system_config.rb:110 to commit
and date information. This information can be useful when debugging
formulae in custom taps to ensure the tap has been correctly updated
recently or to suss out important differences from one version of a tap
to another.

This removes the need to ask users to run something like

    git -C $(brew --repository)/Library/Taps/<tap> show -s --decorate

Close https://github.com/Homebrew/brew/issues/18381

Library/Homebrew/cmd/tap-info.rb

@@ -76,6 +76,10 @@ module Homebrew
               info += "\nPrivate" if tap.private?
               info += "\n#{tap.path} (#{tap.path.abv})"
               info += "\nFrom: #{tap.remote.presence || "N/A"}"
+              info += "\norigin: #{tap.remote}" if tap.remote != tap.default_remote
+              info += "\nHEAD: #{tap.git_head || "(none)"}"
+              info += "\nlast commit: #{tap.git_last_commit || "never"}"
+              info += "\nbranch: #{tap.git_branch || "(none)"}" if tap.git_branch != "master"
             else
               info += "Not installed"
             end

Library/Homebrew/tap.rb

@@ -881,6 +881,9 @@ class Tap
       hash["remote"] = remote
       hash["custom_remote"] = custom_remote?
       hash["private"] = private?
+      hash["HEAD"] = git_head || "(none)"
+      hash["last_commit"] = git_last_commit || "never"
+      hash["branch"] = git_branch || "(none)"
     end
 
     hash