Replace file_name property with get_file_name function

[SergeyYakubov]

Following discussions in #16702, this PR replaces .file_name property with get_file_name function so that later on we could pass parameters to this function (control pulling from an object store, pass user object for authentication, ... ). No functionality changes in this PR.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[jdavcs]

Thank you, @SergeyYakubov - this is a ton of work! Sorry for the long wait; at first I wasn't entirely sure whether these changes may or may not cause problems for serialized dataset objects - but now I see that's not the case. Looks good!

[github-actions]

This PR was merged without a "kind/" label, please correct.