Enable FETCHCONTENT packages using FETCHCONTENT in cmake

[jiaxshi]

Backgrould:
Many ROS xxx-vendor packages download source code via FETCHCONTENT in cmake process. But FETCHCONTENT is disabled by default in yocto.

    -DFETCHCONTENT_FULLY_DISCONNECTED=ON \

In some recipes of meta-ros, reset SRC and revision to download source code with bitbake. Then we need to manually check and update revision/version of these packages. Or we will encounter mismatch problems, such as #1310 .

I propose to use EXTRA_OECMAKE:append = " -DFETCHCONTENT_FULLY_DISCONNECTED=OFF" in all the bbappends, then we don't need to maintain SRC and revision.

[vermaete]

I would not do this.

Some people using Yocto and ROS are working in air gapped networks. To useful stuff in Yocto to handle this will not work when allowing fetching of code after the do_fetch.
Another reason is that reproducible builds become difficult when code is fetched during do_compile instead of do_fetch.

Br

[robwoolley]

Thanks for highlighting this @jiaxshi. As @vermaete said, we need to support an airgap environment, particularly for people that want to be able to maintain a particular release past its end-of-life date. This did help point out a mistake that I made in duplicating the SRCREV in the bbappend. I did this because of recent changes to how AUTOREV works, however I should have just done: SRCREV_foobar = "${SRCREV}" I made this change in mcap and 1 or 2 other packages. It should ease the burden going forward.