[fud2] Add list subcommand

[sampsyo]

Just a really small task from #1878! This new fud2 list command just prints a list of all the registered states and operations, in case you forget a name or whatever.

The current output is:

$ fud2 list
States:
  verilog: .sv .v
  calyx: .futil
  dahlia: .fuse
  mrxl: .mrxl
  dat: .json
  vcd: .vcd
  sim: .exe
  verilog-noverify: .sv
  firrtl: .fir
  primitive-uses-json: .json
  debug:
  xo: .xo
  xclbin: .xclbin

Operations:
  calyx-to-verilog: calyx -> verilog
  dahlia-to-calyx: dahlia -> calyx
  mrxl-to-calyx: mrxl -> calyx
  simulate: sim -> dat
  trace: sim -> vcd
  calyx-noverify: calyx -> verilog-noverify
  icarus: verilog-noverify -> sim
  calyx-to-firrtl: calyx -> firrtl
  firrtl: firrtl -> verilog
  firrtl-noverify: firrtl -> verilog-noverify
  primitive-uses: calyx -> primitive-uses-json
  verilator: verilog -> sim
  interp: calyx -> dat
  debug: calyx -> debug
  xo: calyx -> xo
  xclbin: xo -> xclbin
  xrt: xclbin -> dat
  xrt-trace: xclbin -> vcd

[rachitnigam]

Incredible 👨‍🍳