Clean up remaining deprecated/obsolete features used by the CMake scripts

[jphickey]

Is your feature request related to a problem? Please describe.
In recent years the CMake build has been adopting the current best-practices whenever feasible to do so, and moving away from features that have been marked as obsolete or deprecated.

• Use interface properties to propagate compiler flags, definitions, etc to dependencies, rather than setting "magic variables" that need to be known by the dependency
• Prefer target_include_directories as opposed to include_directories at directory scope
• Prefer target_compile_definitions as opposed to add_definitions at directory scope
• Use of target_link_libraries should include the scope keyword (PUBLIC/PRIVATE) rather than the "bare" signature (also noted by CFE user in add_cfe_app uses deprecated call to target_link_libraries cFE#2141)

Describe the solution you'd like
In particular - the following specific areas should be modernized:

• Public API location should be an interface library:

  osal/CMakeLists.txt

  Line 89 in 38559d4

  include_directories(${OSAL_API_INCLUDE_DIRECTORIES})

• Management of impl-specific flags can also be done via interface library rather than manual propagation here:

  osal/CMakeLists.txt

  Lines 154 to 163 in 38559d4

  	get_directory_property(OSAL_BASE_COMPILE_DEFINITIONS COMPILE_DEFINITIONS)
  	get_target_property(OSAL_BSP_COMPILE_DEFINITIONS osal_${OSAL_SYSTEM_BSPTYPE}_impl INTERFACE_COMPILE_DEFINITIONS)
  	set(OSAL_COMPILE_DEFINITIONS)
  	if (OSAL_BASE_COMPILE_DEFINITIONS)
  	list(APPEND OSAL_COMPILE_DEFINITIONS ${OSAL_BASE_COMPILE_DEFINITIONS})
  	endif (OSAL_BASE_COMPILE_DEFINITIONS)
  	if (OSAL_BSP_COMPILE_DEFINITIONS)
  	list(APPEND OSAL_COMPILE_DEFINITIONS ${OSAL_BSP_COMPILE_DEFINITIONS})
  	endif (OSAL_BSP_COMPILE_DEFINITIONS)
  	set_directory_properties(PROPERTIES COMPILE_DEFINITIONS "${OSAL_COMPILE_DEFINITIONS}")

• Use scope keyword on link libraries:

  osal/CMakeLists.txt

  Line 282 in 38559d4

  target_link_libraries(osal osal_bsp)

• Implement UT coverage interface library as alternative to "flag variables" exported here:

  osal/CMakeLists.txt

  Lines 354 to 355 in 38559d4

  	set(UT_COVERAGE_COMPILE_FLAGS "${UT_COVERAGE_COMPILE_FLAGS}" PARENT_SCOPE)
  	set(UT_COVERAGE_LINK_FLAGS "${UT_COVERAGE_LINK_FLAGS}" PARENT_SCOPE)

Additional context
It is not currently possible to propagate the UT coverage flags if OSAL and the application are in separate builds.

Using the target-scope features and interface libraries is of particular benefit to making a proper OSAL "package" that can be compiled and linked separately from the application (see #1284)

Requester Info
Joseph Hickey, Vantage Systems, Inc.