Set default size for file chooser dialog

Don't take the entire screen space for this dialog when it's ran first time. Also, make it more convenient to use on systems without dconf.
2 jobs for file-chooser-default-size in 7 minutes and 21 seconds (queued for 1 second)
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passed #220626
build

00:07:21

manual #220627
win32 allowed to fail manual
msys2-mingw32