fix: canonicalize all positional args in @named

[ven-k]

• So far, only the 1st positional-arg was canonicalized. This PR canonicalizes all positional args in @named
• Add relevant tests.

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

• @mtkmodel uses @named under the hood. Hence this PR closes Failure to propagate default parameter value to inner system #2294

[ven-k]

Earlier:

julia> @mtkmodel LevelThree begin
           @variables begin
               x(t)
               y(t)
               z(t)
           end
       end
ModelingToolkit.Model{typeof(__LevelThree__), Dict{Symbol, Any}}(__LevelThree__, Dict{Symbol, Any}(:variables => Dict{Symbol, Dict{Symbol, Any}}(:y => Dict(), :z => Dict(), :x => Dict()), :kwargs => Dict{Symbol, Any}(:y => nothing, :z => nothing, :x => nothing), :independent_variable => t), false)

julia>

julia> @parameters begin
           l
           m
           n
       end
3-element Vector{Num}:
 l
 m
 n

julia> @macroexpand1 @named three = LevelThree(x = l, y = m, z = n)
:(three = begin
          #= C:\Users\user\.julia\packages\ModelingToolkit\66mEN\src\systems\abstractsystem.jl:1002 =#
          var"#####__is_system_construction####774" = LevelThree isa DataType && LevelThree <: ModelingToolkit.AbstractSystem
          #= C:\Users\user\.julia\packages\ModelingToolkit\66mEN\src\systems\abstractsystem.jl:1003 =#
          LevelThree(y = m, z = n; name = :three, x = if var"#####__is_system_construction####774"
                      l
                  else
                      (ModelingToolkit.default_to_parentscope)(l)
                  end)
      end)

Now:

@mtkmodel LevelThree begin
    @variables begin
        x(t)
        y(t)
        z(t)
    end
end

@parameters begin
    l
    m
    n
end
@macroexpand1 @named three = LevelThree(x = l, y = m, z = n)
:(three = begin
          #= C:\Users\user\.julia\dev\ModelingToolkit.jl\src\systems\abstractsystem.jl:1002 =#    
          var"#####__is_system_construction####297" = LevelThree isa DataType && LevelThree <: ModelingToolkit.AbstractSystem
          #= C:\Users\user\.julia\dev\ModelingToolkit.jl\src\systems\abstractsystem.jl:1003 =#    
          LevelThree(; name = :three, x = if var"#####__is_system_construction####297"
                      l
                  else
                      (ModelingToolkit.default_to_parentscope)(l)
                  end, y = if var"#####__is_system_construction####297"
                      m
                  else
                      (ModelingToolkit.default_to_parentscope)(m)
                  end, z = if var"#####__is_system_construction####297"
                      n
                  else
                      (ModelingToolkit.default_to_parentscope)(n)
                  end)
      end)