Change msg parameter to use `ref`.
Add test for existing extern(C++) interface cast error.
Add test for class qualifier cast in @safe code.
Add test for casting with opaque array element type.
Fix Issue 23957 - Casting to derived extern(C++) class is unsafe
Signed-off-by: Nicholas Wilson <thewilsonator@users.noreply.github.com>
Merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>