Reduce required Windows CMake version to 3.14 (#89390)

When we landed the CMake minimum requirement constraint for Visual
Studio 2019, we landed it with minimum version 3.15, since that's what
was shipping with the current version of VS 2019 at the time. Looking at
the release notes of earlier versions, it's clear that earlier versions
of Visual Studio 2019 shipped with version 3.14. See:
https://devblogs.microsoft.com/cppblog/visual-studio-cmake-support-clang-llvm-cmake-3-14-vcpkg-and-performance-improvements/

Looking at release notes for CMake 3.15, there are no features/fixes
introduced in that version that we are dependent on.
https://cmake.org/cmake/help/latest/release/3.15.html

Issue: https://github.com/flutter/flutter/issues/88589

dev/integration_tests/flutter_gallery/windows/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(flutter_gallery LANGUAGES CXX)
 
 set(BINARY_NAME "flutter_gallery")

dev/integration_tests/flutter_gallery/windows/flutter/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 
 set(EPHEMERAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/ephemeral")
 

dev/integration_tests/flutter_gallery/windows/runner/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(runner LANGUAGES CXX)
 
 add_executable(${BINARY_NAME} WIN32

dev/manual_tests/windows/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(manual_tests LANGUAGES CXX)
 
 set(BINARY_NAME "manual_tests")

dev/manual_tests/windows/flutter/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 
 set(EPHEMERAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/ephemeral")
 

dev/manual_tests/windows/runner/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(runner LANGUAGES CXX)
 
 add_executable(${BINARY_NAME} WIN32

examples/api/windows/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(dartpad_curve2_d_0 LANGUAGES CXX)
 
 set(BINARY_NAME "dartpad_curve2_d_0")

examples/api/windows/flutter/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 
 set(EPHEMERAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/ephemeral")
 

examples/api/windows/runner/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(runner LANGUAGES CXX)
 
 add_executable(${BINARY_NAME} WIN32

packages/flutter_tools/lib/src/windows/build_windows.dart

@@ -22,7 +22,7 @@ import '../migrations/cmake_custom_command_migration.dart';
 import 'install_manifest.dart';
 import 'visual_studio.dart';
 
-// From https://cmake.org/cmake/help/v3.15/manual/cmake-generators.7.html#visual-studio-generators
+// From https://cmake.org/cmake/help/v3.14/manual/cmake-generators.7.html#visual-studio-generators
 // This may need to become a getter on VisualStudio in the future to support
 // future major versions of Visual Studio.
 const String _cmakeVisualStudioGeneratorIdentifier = 'Visual Studio 16 2019';

packages/flutter_tools/templates/app_shared/windows.tmpl/CMakeLists.txt.tmpl

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project({{projectName}} LANGUAGES CXX)
 
 set(BINARY_NAME "{{projectName}}")

packages/flutter_tools/templates/app_shared/windows.tmpl/flutter/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 
 set(EPHEMERAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/ephemeral")
 

packages/flutter_tools/templates/app_shared/windows.tmpl/runner/CMakeLists.txt

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 project(runner LANGUAGES CXX)
 
 add_executable(${BINARY_NAME} WIN32

packages/flutter_tools/templates/plugin/windows.tmpl/CMakeLists.txt.tmpl

-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.14)
 set(PROJECT_NAME "{{projectName}}")
 project(${PROJECT_NAME} LANGUAGES CXX)