Add caching to the github workflows

[neilenns]

Fixes #185

Our github workflows take around 30 minutes to build right now. This is because of four slow parts:

• Installing vcpkg
• Building afv-native
• Installing node modules
• Downloading electron-builder dependencies

There's also an additional unnecessary npm install step that, while short, does add some time that could be saved and was removed.

This PR adds caching for all of those items:

• vcpkg: Cached in release and CI builds using the vcpkg.json and vcpkg submodule SHA as the hash key
• afv-native: Cached in CI builds using all the files under backend/, the afv-native submodule SHA, and the libuiohook submodule SHA, as the hash key
• node modules: Cached in CI and release builds using the built-in caching mechanism of actions/setup-node
• electron-builder dependencies: Cached in release and CI builds using package-lock.json as the hash key

This cuts the build time down from 30 minutes to around 2 minutes for mac and linux and 3 minutes for windows (which is always slower for some reason).

[neilenns]

This now handles the new libuiohook native dependency.