Bluetooth OPP: Allow sending all mime-types for handover.

This change allows sending of all mime-types through
ACTION_HANDOVER_SEND and ACTION_HANDOVER_SEND_MULTIPLE.
These intent actions are only used by NFC when doing
handover transfers, and require the whitelisting
permission that is only granted to system applications.

Similarly, for receiving, we will still reject certain
mimetypes, except if the transfer was whitelisted because
it was a handover transfer.

At this moment, only the NFC service has the signature
permission required for whitelisting.

This change also allows to send files without extension,
as long as OPP has a valid mimeType. This is useful when
using OPP in combination with a content provider, which
may specify filenames without any extension but with a
valid mime-type.

Bug: 6561169
Change-Id: Ia39418de6bcb2f8af678c7b8637b63b1697eb493