IRShow: Print type of arg0 for invoke when necessary

When invoking any "functor-like", such as a closure:
```julia
bar(x) = @noinline ((y)->x+y)(x)
```
our IR printing was not showing the arg0 invoked, even when it is
required to determine which MethodInstance this is invoking.

Before:
```
julia> @code_typed optimize=true bar(1)
CodeInfo(
1 ─ %1 = %new(var"#bar##2#bar##3"{Int64}, x)::var"#bar##2#bar##3"{Int64}
│   %2 =    invoke %1(x::Int64)::Int64
└──      return %2
) => Int64
```

After:
```
julia> @code_typed optimize=true bar(1)
CodeInfo(
1 ─ %1 = %new(var"#bar##2#bar##3"{Int64}, x)::var"#bar##2#bar##3"{Int64}
│   %2 =    invoke (%1::var"#bar##2#bar##3"{Int64})(x::Int64)::Int64
└──      return %2
) => Int64
```

Author: topolarity

Compiler/src/ssair/show.jl

@@ -105,11 +105,30 @@ function print_stmt(io::IO, idx::Int, @nospecialize(stmt), code::Union{IRCode,Co
             printstyled(io, "dynamic invoke "; color = :yellow)
             abi = (ci::Core.MethodInstance).specTypes
         end
-        show_unquoted(io, stmt.args[2], indent)
-        print(io, "(")
         # XXX: this is wrong if `sig` is not a concretetype method
         # more correct would be to use `fieldtype(sig, i)`, but that would obscure / discard Varargs information in show
         sig = abi == Tuple ? Core.svec() : Base.unwrap_unionall(abi).parameters::Core.SimpleVector
+        f = stmt.args[2]
+        ft = maybe_argextype(f, code, sptypes)
+
+        # We can elide the type for arg0 if it...
+        skip_ftype = (length(sig) == 0) # doesn't exist...
+        skip_ftype = skip_ftype || (
+            # ... or, f prints as a user-accessible value...
+            (f isa GlobalRef) &&
+            # ... and matches the value of the singleton type of the invoked MethodInstance
+            (singleton_type(ft) === singleton_type(sig[1]) !== nothing)
+        )
+        if skip_ftype
+            show_unquoted(io, f, indent)
+        else
+            print(io, "(")
+            show_unquoted(io, f, indent)
+            print(io, "::", sig[1], ")")
+        end
+
+        # Print the remaining arguments (with type annotations from the invoked MethodInstance)
+        print(io, "(")
         print_arg(i) = sprint(; context=io) do io
             show_unquoted(io, stmt.args[i], indent)
             if (i - 1) <= length(sig)