Update CFE to use OS time conversion/access methods

[jphickey]

Is your feature request related to a problem? Please describe.
CFE is directly accessing specific fields within OS_time_t which will break when the struct definition changes.

Describe the solution you'd like
Instead of directly accessing the seconds and microsecs fields within OS_time_t, use the accessor functions to convert/extract the relevant info from the value instead.

Additional context
see nasa/osal#429

Requester Info
Joseph Hickey, Vantage Systems, Inc.

[jphickey]

Also worth noting here that the CFE_TIME_Micro2SubSecs and CFE_TIME_Sub2MicroSecs are fairly broken. I had never really tested/looked at them with any level of detail until now.

There are plenty of values that do not convert to the "ideal" value. For instance the CFE_TIME unit test uses a microsecond value of "567890", for which CFE_TIME_Micro2SubSecs() returns a value of 0x91614000 ... but the closest value by my calculation 0x91613d32 ... the former converts back to 567890.167236us, but the latter converts back to 567890.0000064us - so much closer to the real value.

Of course in this case when CFE_TIME_Sub2MicroSecs rounds it back to an integer, it returns the same original value (567890) but this isn't always the case.

EXAMPLE: At a value of 568017us, CFE_TIME_Micro2SubSecs() returns a value of 0x91699000 (568017.00592) ... the CFE_TIME_Sub2MicroSecs function then converts this back to 568016, not 568017 as was the original value. (FWIW, by my calculation closest/correct value should actually be 0x91698fe7 here, which is 568017.0001us).

My suggestion is to provide OSAL functions that actually implement this properly.