Cleanup deadline code

[rachitnigam]

#398 has a bunch of code that was written during a deadline and needs to be cleaned up.

• Adds XLS as a gen tool (separate branch).
• Adds XLS to the Dockerfile (new issue b/c the problem is that bazel only seems to work on x86. We need to install the arm64 version based on the build)
• Adds the various FFT implementation (only the pure Filament implementation should be in the repo. Others should go in the evaluation repo)
• Uses verible to rename the modules generated by flopoco so they don't clash (separate branch, @UnsignedByte will create an issue)
  • Current, this just does random name mangling using verible. Maybe slang is a better option?
• It adds a primitive to merge values to the same wire (@UnsignedByte can you make an issue describing exactly what this is?)
  • Can this be implemented purely in Filament?
• Add a way to specify global values used in the gen framework #427
  • This seems like a generally useful mechanism but we need to be careful because it might pollute names defined by each tool