Add a python script to install Direct3D 12 SDK components.

This makes it much faster to get started with Direct3D 12 builds,
as you only need to run `python .\misc\scripts\install_d3d12_sdk_windows.py`
then run `scons d3d12=yes`.

This installs DirectX Shader Compiler, Mesa NIR, WinPixEventRuntime
and DirectX 12 Agility SDK.

- Define a default path that uses the locations from the script.
- Now the default path is in "%LOCALAPPDATA%\Godot\build_deps\"
- Updated CI to use this new python script.

Co-Authored-By: Hugo Locurcio <hugo.locurcio@hugo.pro>