Debug builds (and testing) with asserts should exist in all platforms

I was recently tipped (CC manordheim) that our CI is mostly doing release builds. This has caused bugs to slip through (QTBUG-129448) and is dangerous for leaving subtle bugs undetected as asserts are in the code for a good reason, ensuring that the code never enters indeterminate state.

I went through the configurations in qtbase, and I see only 1 linux build (besides ASAN) being debug with tests, and only 1 on macos.

Reasons:

• Too many builds have explicit -release flag
• A non developer-build is by default a release build
  • Can we change our cmake scripts to default to debug build, unless -release is provided?
• Many of the developer-builds have explicit -release flag
• Some platforms build -debug-and-release but they build tests only RelWithDebInfo

Solution: The default mode for a configuration added to the CI should be debug
if we care about CI catching bugs early...

Doing release builds is of course needed for releasing.

• Only the configurations that produce release binaries should be in release mode
• They only need to be in release mode when release binaries are generated.