[REPL] Do not corrupt input when using numbered_prompt! mode (#59730)

Fix the unbounded possible corruption of the user input by reverting to
a non-scoped begin instead of let.

```julia
julia> ex = Base.remove_linenums!(:(using A; using B; using C)); REPL.Numbered.get_usings!([], ex)
2-element Vector{Any}:
 :(using A)
 :(using C)

julia> ex
quote
    using B
end
```

Author: vtjnash

stdlib/REPL/src/REPL.jl

@@ -1845,25 +1845,10 @@ function repl_eval_counter(hp)
 end
 
 function out_transform(@nospecialize(x), n::Ref{Int})
-    return Expr(:toplevel, get_usings!([], x)..., quote
-        let __temp_val_a72df459 = $x
-            $capture_result($n, __temp_val_a72df459)
-            __temp_val_a72df459
-        end
-    end)
-end
-
-function get_usings!(usings, ex)
-    ex isa Expr || return usings
-    # get all `using` and `import` statements which are at the top level
-    for (i, arg) in enumerate(ex.args)
-        if Base.isexpr(arg, :toplevel)
-            get_usings!(usings, arg)
-        elseif Base.isexpr(arg, [:using, :import])
-            push!(usings, popat!(ex.args, i))
-        end
-    end
-    return usings
+    return Expr(:block, # avoid line numbers or scope that would leak into the output and change the meaning of x
+        :(local __temp_val_a72df459 = $x),
+        Expr(:call, capture_result, n, :__temp_val_a72df459),
+        :__temp_val_a72df459)
 end
 
 function create_global_out!(mod)