cask: read installed_version from Info.plist when sensible.

If you're trying to use `brew info --json=v2` to get an installed
version and figure out if it is outdated: you're going to have a bad
time with `auto_updates` casks because `installed_version` is not
actually consistent with the installed version of the app.

Instead, in these cases, try to read from `Info.plist` if there is one
and use that version.

While we're here, add a `blank?` method to `Version` so we can use it
for `present?` checks (making a `null?` `Version` object `blank?`).

Library/Homebrew/cask/cask.rb

@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 
 require "attrable"
+require "bundle_version"
 require "cask/cask_loader"
 require "cask/config"
 require "cask/dsl"
@@ -176,8 +177,19 @@ def installed_caskfile
 
     sig { returns(T.nilable(String)) }
     def installed_version
+      if auto_updates &&
+         (bundle = artifacts.find { |a| a.is_a?(Artifact::App) }&.target) &&
+         (plist = Pathname("#{bundle}/Contents/Info.plist")) &&
+         plist.exist? &&
+         (bundle_version = ::Homebrew::BundleVersion.from_info_plist(plist)) &&
+         (bundle_short_version = bundle_version.short_version.presence)
+        return bundle_short_version
+      end
+
+      return unless (installed_caskfile = self.installed_caskfile)
+
       # <caskroom_path>/.metadata/<version>/<timestamp>/Casks/<token>.{rb,json} -> <version>
-      installed_caskfile&.dirname&.dirname&.dirname&.basename&.to_s
+      installed_caskfile.dirname.dirname.dirname.basename.to_s
     end
 
     def config_path

Library/Homebrew/version.rb

@@ -94,6 +94,9 @@ def numeric?
     def null?
       false
     end
+
+    sig { returns(T::Boolean) }
+    def blank? = null?
   end
 
   # A pseudo-token representing the absence of a token.
@@ -127,6 +130,9 @@ def null?
       true
     end
 
+    sig { returns(T::Boolean) }
+    def blank? = true
+
     sig { override.returns(String) }
     def inspect
       "#<#{self.class.name}>"