Allow dub to be run with OpenD compiler

[SingingBush]

I am aware that there may not be much incentive for this but it would be helpful if dub could be used with OpenD.

Currently if I attempt to use dub with the opend binary (dub --compiler=opend), it'll just error as it's an unknown compiler:

Error Unknown compiler: ../tools/opend-jan2026/bin/opend

I cloned the dub repo and created a OpenDCompiler class based off of the one for dmd with a few other changes and was able to get a build that would allow me to compile a dub based project using OpenD.

I'm happy to make a PR for it if it'll be considered for merging

[WebFreak001]

as temporary workaround, maybe try just symlinking to it and name the symlink dmd - it could be enough to make dub run the compiler as dmd