std: find a better home for the "preopens" concept

doc/langref/wasi_preopens.zig

@@ -1,10 +1,8 @@
 const std = @import("std");
 
-pub fn main(init: std.process.Init) !void {
-    const preopens = try std.fs.wasi.preopensAlloc(init.arena.allocator());
-
-    for (preopens.names, 0..) |preopen, i| {
-        std.debug.print("{d}: {s}\n", .{ i, preopen });
+pub fn main(init: std.process.Init) void {
+    for (init.preopens.map.keys(), 0..) |preopen, i| {
+        std.log.info("{d}: {s}", .{ i, preopen });
     }
 }