Show basic block statement ranges in CFG output [NFC]

[maleadt]

The CFG show output was not immediately obvious to me, so annotate it, and include statement ranges:

julia> # get some ir
       function foo(i)
           j = i+42
           j == 1 ? 1 : 2
       end

julia> ir = only(Base.code_ircode(foo, (Int,)))[1]
3 1 ─ %1 = Base.add_int(_2, 42)::Int64
4 │   %2 = (%1 === 1)::Bool
  └──      goto #3 if not %2
  2 ─      return 1
  3 ─      return 2

julia> ir.cfg
1	=>	3, 2
2	=>
3	=>


julia> using Revise
julia> Revise.track(Base)

julia> ir.cfg
CFG with 3 blocks:
  bb 1 (stmts 1:3) ⇨ bb 3, 2
  bb 2 (stmt 4)
  bb 3 (stmt 5)

Feel free to bikeshed or give ideas on how to further improve the output.

[gbaraldi]

This looks cool but I think I prefer the old arrows instead of the unicode ones. Maybe use ⇨ instead of the thin one?

[maleadt]

⇨ looks pretty tiny in monospace font (see above).