Add support for Base.ImmutableDict

[danielmatz]

I tried to use Accessors with Base.ImmutableDict:

julia> x = Base.ImmutableDict("a" => 1, "b" => 2)
Base.ImmutableDict{String, Int64} with 2 entries:
  "b" => 2
  "a" => 1

julia> @set x["b"] = 3
ERROR: MethodError: no method matching empty!(::Base.ImmutableDict{String, Int64})
The function `empty!` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  empty!(::ComputePipeline.ComputeGraph)
   @ ComputePipeline ~/.julia/packages/ComputePipeline/03tW7/src/ComputePipeline.jl:1041
  empty!(::Scene; reset_theme)
   @ Makie ~/.julia/packages/Makie/4JW9B/src/scenes.jl:471
  empty!(::Compiler.CompilationQueue)
   @ Base ~/.julia/juliaup/julia-1.12.0+0.aarch64.apple.darwin14/share/julia/Compiler/src/typeinfer.jl:1333
  ...

Stacktrace:
 [1] copy!(dst::Base.ImmutableDict{String, Int64}, src::Base.ImmutableDict{String, Int64})
   @ Base ./abstractdict.jl:200
 [2] setindex
   @ ~/.julia/packages/Accessors/8Y4uq/src/setindex.jl:22 [inlined]
 [3] set(obj::Base.ImmutableDict{String, Int64}, lens::IndexLens{Tuple{String}}, val::Int64)
   @ Accessors ~/.julia/packages/Accessors/8Y4uq/src/optics.jl:417
 [4] top-level scope
   @ REPL[62]:1

It would be nice to add support for Base.ImmutableDict.

[aplavin]

Yes, should be simple: define the proper setindex method here https://github.com/JuliaObjects/Accessors.jl/blob/master/src/setindex.jl.

Btw, you might want to add Base.setindex() method for immutabledict to Julia Base itself!