destructuring in function argument breaks macro expansion

[simeonschaub]

We unintentionally leak x as a global here:

julia> macro _macroexpand(x, m=__module__)
           :($__source__; macroexpand($m, Expr(:var"hygienic-scope", $(esc(Expr(:quote, x))), $m)))
       end
@_macroexpand (macro with 2 methods)

julia> @_macroexpand f((x,)) = x
:(Main.f((Main.x,)) = begin
          #= REPL[4]:1 =#
          Main.x
      end)

Not only does this have potentially bad side effects, but it also worsens performance due to converting x to a global. Property destructuring has the same issue, but currently errors loudly until #48726 is addressed.