Jacques Lucke
f86331a033
For some underlying data (e.g. spans) we had two virtual array implementations. One for the mutable and one for the immutable case. Now that most code does not deal with the virtual array implementations directly anymore (since rBrBd4c868da9f97a), we can get away with sharing one implementation for both cases. This means that we have to do a `const_cast` in a few places, but this is an implementation detail that does not leak into "user code" (only when explicitly casting a `VArrayImpl` to a `VMutableArrayImpl`, which should happen nowhere).