Implemented safer C++ DataContainer data type handling, fixes #1193

[evgueni-ovtchinnikov]

Changes in this pull request

Current C++ DataContainer classes use static casts of void* pointers, which may be unsafe (cf. #1193).

This PR implements an alternative template-based design whereby static casts are only used on C interface level, which is not supposed to be used by SIRF users.

Testing performed

Related issues

Fixes #1193

Checklist before requesting a review

• [ ] I have performed a self-review of my code
• [ ] I have added docstrings/doxygen in line with the guidance in the developer guide
• [x] I have implemented unit tests that cover any new or modified functionality
• [x] The code builds and runs on my machine
• [ ] CHANGES.md has been updated with any functionality change

Contribution Notes

Please read and adhere to the contribution guidelines.

Please tick the following:

• [x] The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in SIRF (the Work) under the terms and conditions of the Apache-2.0 License.

[evgueni-ovtchinnikov]

Left unattended for a long time, resulting in weird conflicts with master. Taken over by PR #1210.