Implement Windows incremental build cache

[DanRStevens]

Relates to:

• Speed up Windows CI OutpostUniverse/OPHD#1418

Implements incremental build caching for Windows feature branches. This can drastically reduce the build time on feature branches, depending on how much code has changed. A full build might take 3.5 - 4 minutes. An incremental build with no changes might take 1 - 1.5 minutes.

The default branch will always do a fresh full build, without attempting to load a cache. This is to ensure a full build will always work, and to prevent any caching artifacts from accumulating over time, such as caching old files that are no longer needed, but never explicitly deleted from the build folder. The build time of the default branch is less critical, since builds there are only done after work on PRs is completed and merged, so it doesn't typically hold up additional work.