This removes the ability to use ConfigurationData as a dict, but
restricting the inputs to `str | int | bool`. This may be a little too
soon for this, and we may want to wait on that part, it's only bee 8
months since we started warning about this.
D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
It seems that some projects relied on the previously buggy
behaviour of accepting a 2-element list as the single argument
to configuration_data.set().
Special-case this behaviour, and emit a deprecation message.