Prior to this commit, UrlResource#getFilename() returned the filename
of the resource URL-encoded which is in contrast to what
FileSystemResource#getFilename() returns for an equivalent resource.
In addition, users most likely expect that a filename returned from a
method defined in the Resource interface is unencoded.
This commit therefore revises UrlResource#getFilename() so that it
always returns the filename URL-decoded.
Closes gh-29261
0aa9d9d535