cmake: re-add simple test target, and name it `tests`

cmake: re-add simple test target, and name it `tests`

Before this patch there was no (easy) way to run tests without various
verbose options, hindering readability of the output due its length.

Unfortunately CMake reserves `test` as a target name, which was
the reason for its removal earlier. Re-add it with the name `tests`,
to have the functionality without the name collision.

Also add a `tests` target as an alias to `test` for autotools.

Ref: https://cmake.org/cmake/help/v4.1/policy/CMP0037.html
Follow-up to cfea4f2f4dc316c38694440ef2eed899a3e7d207 #6258
Closes #18145