Merge bitcoin/bitcoin#31173: cmake: Add FindQRencode module and enable libqrencode package for MSVC

9e5089dbb0 build, msvc: Enable `libqrencode` vcpkg package (Hennadii Stepanov)
30089b0cb6 cmake: Add `FindQRencode` module (Hennadii Stepanov)

Pull request description:

  This PR introduces the `FindQRencode` CMake module, following the official CMake [guidelines](https://cmake.org/cmake/help/latest/manual/cmake-developer.7.html#find-modules) for managing [upstream libraries](https://github.com/fukuchi/libqrencode) that lack a config file package. This module enhances flexibility in locating the `libqrencode` library by making the use of `pkg-config` optional.

  With this update, `libqrencode` can be detected on systems where either `pkg-config` or the `libqrencode.pc` file is unavailable, such as Windows environments using the vcpkg package manager. However, if `libqrencode.pc` is available, it remains beneficial as the only direct source of the library's version information.

  Additionally, the `libqrencode` vcpkg package is enabled for MSVC builds.

  Here is a diff for configuration output on Ubuntu 24.10:
  ```diff
   -- Detecting CXX compile features - done
   -- Found SQLite3: /usr/include (found suitable version "3.46.1", minimum required is "3.7.17")
   -- Found PkgConfig: /usr/bin/pkg-config (found version "1.8.1")
  --- Checking for module 'libqrencode'
  ---   Found libqrencode, version 4.1.1
  +-- Found QRencode: /usr/lib/x86_64-linux-gnu/libqrencode.so (found version "4.1.1")
   -- Found Qt: /usr/lib/x86_64-linux-gnu/cmake/Qt5 (found suitable version "5.15.15", minimum required is "5.11.3")
   -- Performing Test CXX_SUPPORTS__WERROR
   -- Performing Test CXX_SUPPORTS__WERROR - Success
  ```

ACKs for top commit:
  fanquake:
    ACK 9e5089dbb0

Tree-SHA512: bb9baca64386772f2f4752b1cbff1230792562ca6b2e37c56ad28580b55b1ae6ff65c2cf0d8ab026111d7b5a056d7ac672496a3cfd1a81e4fdd2b84c8cf75fff

CMakeLists.txt

@@ -135,8 +135,7 @@ cmake_dependent_option(ENABLE_EXTERNAL_SIGNER "Enable external signer support."
 
 cmake_dependent_option(WITH_QRENCODE "Enable QR code support." ON "BUILD_GUI" OFF)
 if(WITH_QRENCODE)
-  find_package(PkgConfig REQUIRED)
-  pkg_check_modules(libqrencode REQUIRED IMPORTED_TARGET libqrencode)
+  find_package(QRencode MODULE REQUIRED)
   set(USE_QRCODE TRUE)
 endif()