Merge bitcoin/bitcoin#31851: doc: build: Fix instructions for msvc gui builds

c3fa043 doc: build: Fix instructions for msvc gui builds (David Gumberg)

Pull request description:

  If the instructions in `doc/build-windows-msvc.md` are followed as-is, and "Developer (PowerShell|Command Prompt) for VS 2022" is used to execute the suggested build commands, the root directory of vcpkg (e.g. in VS 2022 Community edition: `C:\Program Files\Microsoft Visual Studio\2022\Community\VC\vcpkg`), is too long, and when vcpkg attempts to build any of the QT packages, it will fail because of build steps that require path lengths greater than Windows' `MAX_PATH` 260 character limit. This can be avoided without needing to move the vcpkg root dir by setting [`--x-buildtrees-root`](https://learn.microsoft.com/en-us/vcpkg/commands/common-options#buildtrees-root) to a short path, like `C:\vcpkg`.

  See e.g. microsoft/vcpkg#28451, microsoft/vcpkg#28083, microsoft/vcpkg#24751.

ACKs for top commit:
  achow101:
    ACK c3fa043
  hebasto:
    ACK c3fa043.
  TheCharlatan:
    ACK c3fa043

Tree-SHA512: 7de11d38b9125de63e72415f79d82f18818123a1b37f679f2229c4c82f5628dd7d1039dbc5dcdf1bc1c8c382e3e29de74a31d256e73872cbf1fa2687c52185ca

Author: achow101

doc/build-windows-msvc.md

@@ -59,6 +59,17 @@ ctest --test-dir build --build-config Release  # Use "-j N" for N parallel tests
 cmake --install build --config Release         # Optional.
 ```
 
+If building with `BUILD_GUI=ON`, vcpkg installation during the build
+configuration step might fail because of extremely long paths required during
+vcpkg installation if your vcpkg instance is installed in the default Visual
+Studio directory. This can be avoided without modifying your vcpkg root
+directory by changing vcpkg's intermediate build directory with the
+`--x-buildtrees-root` argument to something shorter, for example:
+
+```powershell
+cmake -B build --preset vs2022-static -DVCPKG_INSTALL_OPTIONS="--x-buildtrees-root=C:\vcpkg"
+```
+
 ### 5. Building with Dynamic Linking without GUI
 
 ```