TypeScript: Refactor BFast to use Fetch and Stream API

[mavimaec]

TODO

• Consume VIM file HTTP stream using the Fetch API

  • https://developer.mozilla.org/en-US/docs/Web/API/Streams_API/Using_readable_streams

• Unblock the 2GB VIM file loading issue: https://vimdevelopment01storage.blob.core.windows.net/snapshots/V1281-SkanskaTower-R20.vim

[mavimaec]

Possibly do this in the context of .vimx