Fix mechanize vendoring; add RBI defs

Library/Homebrew/dev-cmd/vendor-gems.rb

@@ -61,6 +61,9 @@
         %w[
           mechanize
         ].each do |gem|
+          (HOMEBREW_LIBRARY_PATH/"vendor/gems").cd do
+            Pathname.glob("#{gem}-*/").each { |path| FileUtils.rm_r(path) }
+          end
           ohai "gem install #{gem}"
           safe_system "gem", "install", gem, "--install-dir", "vendor",
                       "--no-document", "--no-wrappers", "--ignore-dependencies", "--force"

Library/Homebrew/download_strategy.rbi

@@ -1,6 +1,18 @@
 # typed: strict
 
 module AbstractDownloadStrategy::Pourable
-  include Kernel
   requires_ancestor { AbstractDownloadStrategy }
 end
+
+class Mechanize::HTTP
+  ContentDisposition = Struct.new :type, :filename, :creation_date,
+    :modification_date, :read_date, :size, :parameters
+end
+
+class Mechanize::HTTP::ContentDispositionParser
+  sig {
+    params(content_disposition: String, header: T::Boolean)
+    .returns(T.nilable(Mechanize::HTTP::ContentDisposition))
+  }
+  def parse(content_disposition, header = false); end
+end