Rename temp file to use a valid image file extension

MediaProvider added a restriction in R for apps targeting SDK 30 to
not allow .tmp files in image file directories such as "Pictures" and
"DCIM". This CL renames the temp file to avoid this restriction.

Also added test to check for writing to FileDescriptor instances.

Bug: 160874777
Test: atest CtsMediaTestCases:android.media.cts.ExifInterfaceTest
    Also tested with an image file inside /Pictures
Change-Id: Iedb548651c0048b0aecc4b34e9c94f778cf5d1e0