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)
```

1 files changed, 2 insertions, 0 deletions

diff --git a/activestorage/test/models/blob_test.rb b/activestorage/test/models/blob_test.rb
index 5cd2a94326..9b555f9a1d 100644
--- a/activestorage/test/models/blob_test.rb
+++ b/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