[wpiutil] Add MessagePack utility functions (#4448)

Also add mpack to srcDirs.

wpiutil/src/main/native/include/wpi/MessagePack.h

@@ -0,0 +1,39 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <stdint.h>
+
+#include <string>
+#include <string_view>
+
+#include "wpi/mpack.h"
+#include "wpi/span.h"
+
+namespace mpack {
+
+inline void mpack_write_str(mpack_writer_t* writer, std::string_view str) {
+  mpack_write_str(writer, str.data(), str.size());
+}
+
+inline void mpack_write_bytes(mpack_writer_t* writer,
+                              wpi::span<const uint8_t> data) {
+  mpack_write_bytes(writer, reinterpret_cast<const char*>(data.data()),
+                    data.size());
+}
+
+inline void mpack_reader_init_data(mpack_reader_t* reader,
+                                   wpi::span<const uint8_t> data) {
+  mpack_reader_init_data(reader, reinterpret_cast<const char*>(data.data()),
+                         data.size());
+}
+
+mpack_error_t mpack_expect_str(mpack_reader_t* reader, std::string* out,
+                               uint32_t maxLen = 1024);
+
+mpack_error_t mpack_read_str(mpack_reader_t* reader, mpack_tag_t* tag,
+                             std::string* out, uint32_t maxLen = 1024);
+
+}  // namespace mpack