The headline here is adding a flatbuffer_ts_library rule for generating
typescript code in bazel. This entails some non-trivial other changes,
but ideally none are user-visible.
In particular:
* Added a --ts-flat-file flag that generates a single *_generated.ts
file instead of separate files for each typescript type. This makes
bazel much happier.
* Import the bazel rules_nodejs stuff needed to support building
typescript in bazel
* Move flatbuffers.ts to index.ts because I wasn't sure how to make
bazel comprehend the "main" attribute of the package.json. Happy
to take another stab at figuring that out if really needed.
* Fix another couple keyword escaping spots in typescript...
