Before this commit, we had the following issue with binary widget in a form:
Suppose we have a binary field with filename attribute set. When uploading a
new file 'temp.txt' with content 'Cg==', the displayed value is 'Cg=='. When
the changes are saved, the displayed value becomes 'temp.txt'.
It should always display 'temp.txt', which is what is fixed by this commit.
In addition to fixing this issue, we describe what is the expected displayed
value of a binary field. This is based on whether the attribute filename is
provided, and whether the record is in edit or read-only mode.
Fixes#21630Closes#24275
Co-authored-by: Nick Booker <nick.booker@opusvl.com>
