Mms: Share image/video files via Messaging from file explorer

When we're handling Intent.ACTION_SEND_MULTIPLE, the type passed
in is "*/*", and share uri will look like this: "file:///" if
share from file explorer. So message application can not identify
the share file's type.

Use MediaFile's function to identify the share file's type and set
attachment.

CRs-Fixed: 496743

Change-Id: Icbf37589fde631a385d548fe86d1ee18aea4a7c8