ASN1: Added support for using #.REGISTER_NEW

This will register BER PDU-dissectors as "new".
Return number of bytes dissected from dissector_try_* functions.
Return number of bytes dissected in DissectorTable:try()

This will make it possible to get dissected length when using
dissector_try_*() and dissected ASN.1 length in Lua when using
DissectorTable:try() (as we already have for Dissector:call).

Change-Id: I8802a812bd484c1e8794c618b87e676003aea94a
Reviewed-on: https://code.wireshark.org/review/4493
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Stig Bjørlykke <stig@bjorlykke.org>