v1.2.0 release

• revamped action into a consolidated CMakeLists.txt approach.
  • in part this was to leverage cmake's ExternalProject_Add functionality, which simplifies "calling out" into the various dependent Khronos repos that basically standardize around cmake already.
• added support for building individual SDK components:
  • Vulkan-Headers
  • Vulkan-Loader
  • Glslang
  • SPIRV-Cross
  • SPIRV-Tools
  • SPIRV-Reflect
  • SPIRV-Headers
• eliminated unnecessary changes to the host project build environment
  • previously building SDK components could end up "polluting" the host project environment on windows (ie: the ninja version that building SDK components themselves depends on becoming the default ninja seen in the PATH)
  • on windows this action now uses humbletim/vsdevenv-shell to very selectively enable build tools for specific internal steps, while leaving the host project environment as unaffected as practical
• now works with the upcoming windows-2022 github actions environment (which will become windows-latest at some point in the future)