Update for Flutter 3.10 beta (#1746)

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [ ] All existing and new tests are passing.

---------

Co-authored-by: David Iglesias <ditman@gmail.com>
Co-authored-by: Mark Thompson <2554588+MarkTechson@users.noreply.github.com>
Co-authored-by: John Ryan <ryjohn@google.com>

desktop_photo_search/fluent_ui/windows/runner/utils.cpp

@@ -47,16 +47,17 @@ std::string Utf8FromUtf16(const wchar_t* utf16_string) {
   }
   int target_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
-      -1, nullptr, 0, nullptr, nullptr);
+      -1, nullptr, 0, nullptr, nullptr)
+    -1; // remove the trailing null character
+  int input_length = (int)wcslen(utf16_string);
   std::string utf8_string;
-  if (target_length == 0 || target_length > utf8_string.max_size()) {
+  if (target_length <= 0 || target_length > utf8_string.max_size()) {
     return utf8_string;
   }
   utf8_string.resize(target_length);
   int converted_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
-      -1, utf8_string.data(),
-      target_length, nullptr, nullptr);
+      input_length, utf8_string.data(), target_length, nullptr, nullptr);
   if (converted_length == 0) {
     return std::string();
   }

desktop_photo_search/fluent_ui/windows/runner/win32_window.cpp

@@ -60,7 +60,7 @@ class WindowClassRegistrar {
  public:
   ~WindowClassRegistrar() = default;
 
-  // Returns the singleton registar instance.
+  // Returns the singleton registrar instance.
   static WindowClassRegistrar* GetInstance() {
     if (!instance_) {
       instance_ = new WindowClassRegistrar();

desktop_photo_search/fluent_ui/windows/runner/win32_window.h

@@ -77,7 +77,7 @@ class Win32Window {
   // OS callback called by message pump. Handles the WM_NCCREATE message which
   // is passed when the non-client area is being created and enables automatic
   // non-client DPI scaling so that the non-client area automatically
-  // responsponds to changes in DPI. All other messages are handled by
+  // responds to changes in DPI. All other messages are handled by
   // MessageHandler.
   static LRESULT CALLBACK WndProc(HWND const window,
                                   UINT const message,