Bug 35640: Upgrade FileSaver JS library to v2.0.4

Bug 35640: Upgrade FileSaver JS library to v2.0.4

This patch upgrades filesaver.js from an unknown version added in 2015
to v2.0.4 which was released in 2020. The patch also moves the asset to
its own directory for consistency's sake.

To test, apply the patch and clear your browser cache if necessary.

- Locate a bibliographic record in the staff interface and edit it.
- Switch to the advanced editor.
- Click the dropdown menu next to the "Save to catalog" button, and test
  both the "Save as MARC" and "Save as MARCXML" controls.
- In both cases the record should be downloaded correctly.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>