Fix #2284, improve add_cfe_tables function

[jphickey]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
Improves the functionality and adds additional documentation about how this function is intended to work. The improvements add some flexibility and intelligence and should be backward compatible with existing use cases.

The add_cfe_app() function now adds an additional interface target that can be referenced when building tables, and this includes the directory-scope properties from the original app build. Therefore, calls to add_cfe_tables from other (non-app) contexts can get the full set of include directories.

This also makes the target name simpler when adding custom properties, it is simply "${APP_NAME}.table"

Finally, instead of invoking the table tool (elf2cfetbl) directly in the context of the table build rule, it generates a custom makefile rule instead, which is called from the top-level (mission) scope to do the conversions.

Fixes #2284

Testing performed
Build and sanity check table builds of CFS apps in a variety of configurations, with and without mission-provided overrides

Expected behavior changes
Updates to how the table tool is actually invoked

System(s) tested on
Debian

Additional context
This also sets up for an easier migration path to EDS-based tables, as in this context the table building process must be run using a host-native compiler rather than the target compiler (because EDS, not the compiler, defines the binary layout).

Contributor Info - All information REQUIRED for consideration of pull request
Joseph Hickey, Vantage Systems, Inc.