Create a setup-build action for both Mac and Windows

[Steelskin]

We need to do different setup for Mac and Windows hosts:

• On Windows, we use compnerd/gha-setup-vsdevenv@main to setup Visual Studio (which includes CMake and ninja as part of the CMake installation)
• On Mac, we seanmiddleditch/gha-setup-ninja@master to setup ninja, since CMake is already installed on the host.

We should have a single action to do both, tentatively called a setup-cmake action that we would depend on.

[Steelskin]

Following further discussions since this was first filed, we are going to go with a setup-build action, which will take care of setting up:

• The Windows SDK version.
• The MSVC version.
• The CMake version.
• Ninja.
• sccache.

The aim is to simplify the build setup in each job and make it easy to test pre-release versions of components like the Windows SDK before they become a problem.