App should treat CFE_SB_MsgId_t values as opaque

[jphickey]

Is your feature request related to a problem? Please describe.
For compatibility going forward, code should not assume that CFE_SB_MsgId_t is an integer.

Describe the solution you'd like
When dealing with an integer, such as when printing in events/messages or for backward compatibility with MID #define's, the code may use CFE_SB_ValueToMsgId() and CFE_SB_MsgIdToValue() conversion routines.

Additional context
Architecturally, the CFE_SB_MsgId_t is supposed to be an opaque/abstract value that identifies an endpoint on the software bus routing domain. The specific meaning of integer values is already different in an "extended header" (CCSDS v2) build vs. the standard header build. Therefore apps should never make assumptions regarding the specific integer values, and all introspection of CFE_SB_MsgId_t values should be through the CFE SB API only.

Requester Info
Joseph Hickey, Vantage Systems, Inc.

[jphickey]

Rebased and pared back changeset to only the parts accepted in CFE.

This actually causes a compile failure on RTEMS when CFE_SB_MsgId_t changes type (extended headers and it goes from uint16 to uint32) so its not just cosmetic.