Fix `blob.service_url` for supports string or nil `:filename` option.

- Make sure `blob.service_url` present a `ActiveStorage::Filename` type to `serivce.url`.
- Add `ActiveStorage::Filename.wrap` method.

before:

```rb
blob.service_url(filename: ActiveStorage::Filename.new("new.txt"))

blob.service_url(filename: "new.txt")
=> NoMethodError: undefined method `parameters' for "new.txt":String

params = {}
blob.service_url(filename: params[:filename])
=> NoMethodError: undefined method `parameters' for nil:NilClass
```

after:

```rb
blob.service_url(filename: "new.txt")
blob.service_url(filename: nil)
```

activestorage/app/models/active_storage/blob.rb

@@ -109,7 +109,9 @@ class ActiveStorage::Blob < ActiveRecord::Base
   # with users. Instead, the +service_url+ should only be exposed as a redirect from a stable, possibly authenticated URL.
   # Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
   # it allows permanent URLs that redirect to the +service_url+ to be cached in the view.
-  def service_url(expires_in: service.url_expires_in, disposition: :inline, filename: self.filename, **options)
+  def service_url(expires_in: service.url_expires_in, disposition: :inline, filename: nil, **options)
+    filename = ActiveStorage::Filename.wrap(filename || self.filename)
+
     service.url key, expires_in: expires_in, filename: filename, content_type: content_type,
       disposition: forcibly_serve_as_binary? ? :attachment : disposition, **options
   end

activestorage/app/models/active_storage/filename.rb

@@ -5,6 +5,14 @@
 class ActiveStorage::Filename
   include Comparable
 
+  class << self
+    # Returns a Filename instance based on the given filename. If the filename is a Filename, it is
+    # returned unmodified. If it is a String, it is passed to ActiveStorage::Filename.new.
+    def wrap(filename)
+      filename.kind_of?(self) ? filename : new(filename)
+    end
+  end
+
   def initialize(filename)
     @filename = filename
   end

activestorage/test/models/blob_test.rb

@@ -82,6 +82,8 @@ class ActiveStorage::BlobTest < ActiveSupport::TestCase
     freeze_time do
       assert_equal expected_url_for(blob), blob.service_url
       assert_equal expected_url_for(blob, filename: new_filename), blob.service_url(filename: new_filename)
+      assert_equal expected_url_for(blob, filename: new_filename), blob.service_url(filename: "new.txt")
+      assert_equal expected_url_for(blob, filename: blob.filename), blob.service_url(filename: nil)
     end
   end