[reg] fix Issue 13084 - ModuleInfo.opApply delegate expects immutable parameter

https://issues.dlang.org/show_bug.cgi?id=13084

Also requires https://github.com/D-Programming-Language/druntime/pull/886

The changes are pretty self-explanatory, it avoids breaking ModuleInfo code because it is now immutable.
Because it's adding dead code to the compiler.  Most of the time this approach does not work, for example msot mangling changes cannot be worked around like this.

Using a tool more powerful than git bisect solves the problem without adding cruft.