Unify target finalizer execution (e.g. auto-linking plugins) for tests across platforms

Currently tests added by functions like qt_internal_add_test / manual_test, etc don't have finalizers executed for them in most cases.

That is not the case for projects that use the public qt_add_executable function.

This causes issues for tests that depend on plugins being auto-linked, or any other finalizer behavior.

Currently, the qt_add_executable finalizers are executed for internal tests on iOS only, which was implemented for QTBUG-104754.

It wasn't enabled for all platforms because webassembly has some custom finalizers running for tests, and there might be duplicate executions if we just enabled the regular finalizers too.

There might also be issues with qml auto-linking on non-cross compile targets, due to qmlimportscanner not being available.

All of these concerns need to be reconciled and unified.