Increase CMake minimum version from 3.9 to 3.16

[mwtoews]

This PR upgrades the CMake minimum version from 3.9 to 3.16. It also removes old workaround and hacks that were needed to support older CMake versions.

Also, fetching the "internal" googletest is modified according to this doc that needs CMake 3.14. (to be resubmitted for a separate PR)

See discussion on mail list.

Related to #3987 (ping @ErixenCruz).
Refer to #1907 for previous CMake bump four years ago.

[rouault]

The error with CIFuzz is unrelated and will be fixed if you rebase on top of latest master

[dg0yt]

Do you also want to migrate from cmake/FindSqlite3.cmake to the official SQLite3?
https://cmake.org/cmake/help/latest/module/FindSQLite3.html

Note that it uses a different set of variable names, and cache variables are used for user input.

[mwtoews]

Thanks for the suggestion @dg0yt . It seems that we'd need to translate (and possibly deprecate) these documented options:

• SQLITE3_INCLUDE_DIR → SQLite3_INCLUDE_DIRS
• SQLITE3_LIBRARY → SQLite3_LIBRARIES

[ErixenCruz]

Vote for CMake 3.16 passed https://lists.osgeo.org/pipermail/proj/2024-January/011235.html. This PR can update FindSQLite3, or we can do it separately in #3987. It may make sense to do it all here in one "3.16 upgrade" PR, but it could go either way

[ErixenCruz]

Do you know why we fetch directly in CMake instead of relying on something like a git submodule? I think git submodule could be simpler/cleaner

[mwtoews]

Thanks for the update @ErixenCruz

I'm going to simplify this PR, and split off FetchContent/googletest and FindSqlite3 upgrades into separate PRs, since these are slightly more complicated and probably deserve a bit more focus/conversation. This PR should cover the ubuntu upgrades and the low-hanging CMake upgrades already done (are there any others?)