SAPDIAG: Added SAP Diag as main dissector

Added the SAP Diag dissector protocol from [SecureAuth's plugin](https://github.com/SecureAuthCorp/SAP-Dissection-plug-in-for-Wireshark/blob/master/src/packet-sapdiag.c).

This is a dissector that implements the Diag protocol. Decompression of packets is not considered as this requires the proprietary LZC/LZH decompression routines still pending to be added in #8973. The Diag packets can be wrapped in an SNC frame, in which case the respective dissector is called. Embedded RFC calls are disabled as this requires the respective dissector to be found, which will be submitted in a separate merge request.

Details about the protocol and example requests can be found in [pysap's documentation](https://pysap.readthedocs.io/en/latest/protocols/SAPDiag.html).

docbook/release-notes.adoc

@@ -89,6 +89,7 @@ The following features are new (or have been significantly updated) since versio
 // git log --oneline --diff-filter=A --stat v3.7.0rc0.. epan/dissectors plugins
 [commaize]
 --
+SAP GUI (SAPDiag)
 SAP Enqueue Server (SAPEnqueue)
 SAP HANA SQL Command Network Protocol (SAPHDB)
 SAP Internet Graphic Server (SAP IGS)

epan/dissectors/CMakeLists.txt

@@ -1775,6 +1775,7 @@ set(DISSECTOR_SRC
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-sadmind.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-sametime.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-sap.c
+	${CMAKE_CURRENT_SOURCE_DIR}/packet-sapdiag.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-sapenqueue.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-saphdb.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-sapigs.c