optimizer: `@nospecialize` annotation doesn't work when applied to unnamed argument

[aviatesk]

julia> @noinline valid(@nospecialize x::Any) = Base.inferencebarrier(0)
valid (generic function with 1 method)

julia> @noinline invalid1(@nospecialize ::Any) = Base.inferencebarrier(0)
invalid1 (generic function with 1 method)

julia> @noinline invalid2(@nospecialize ::Any) = Base.inferencebarrier(0)
invalid2 (generic function with 1 method)

julia> code_typed((Any,)) do x
           valid(x), invalid1(x), invalid2(x)
       end
1-element Vector{Any}:
 CodeInfo(
1 ─ %1 = invoke Main.valid(x::Any)::Any
│   %2 = Main.invalid1(x)::Any
│   %3 = Main.invalid2(x)::Any
│   %4 = Core.tuple(%1, %2, %3)::Tuple{Any, Any, Any}
└──      return %4
) => Tuple{Any, Any, Any}

Here calls to invalid1 and invalid2 should be resolved statically (i.e. resolved to :invoke expressions) since their ::Any-argument is explicitly declared as @nospecialize.

[nsajko]

xref: #55154 (comment)