Thanks to @fearthecowboy for help on this one.

I considered ripping out the rush dependency, since it seems like we are only ever going to have one meaningful "project", and the dependency deduplication we need seems to be already done by pnpm (rather than npm), but after talking with @fearthecowboy I've decided to not go there since we still have rush linking the test project in.

Unfortunately, there does not appear to be an effiicent way to build the typescript parts out-of-source, since they depend on node_modules which is put into the source tree.

This adds a vcpkg.ps1 which does the same "environment hacking" as the in-development ce.ps1, teaches CMakeLists.txt to invoke rush and the typescript compiler as necessary, and teaches vcpkg.exe to use a hard-coded-into-the-binary path to the source tree when that in-development setting is turned on.

The previous "always download latest ce bits" behavior is retained for folks who build vcpkg.exe from source and don't want to arrange for node and rush to be available.

…igger infinite loops.

…k afterwards.