std.json.Value: added dumpStream(), utilize WriteStream for dump()

lib/std/debug.zig

@@ -45,6 +45,7 @@ var stderr_file_out_stream: File.OutStream = undefined;
 
 var stderr_stream: ?*io.OutStream(File.WriteError) = null;
 var stderr_mutex = std.Mutex.init();
+
 pub fn warn(comptime fmt: []const u8, args: ...) void {
     const held = stderr_mutex.acquire();
     defer held.release();
@@ -64,6 +65,10 @@ pub fn getStderrStream() !*io.OutStream(File.WriteError) {
     }
 }
 
+pub fn getStderrMutex() *std.Mutex {
+    return &stderr_mutex;
+}
+
 /// TODO multithreaded awareness
 var self_debug_info: ?DebugInfo = null;