The logic to manage generating typescript in a single file was
generating self imports and unused local names, which triggered some
linters.
This resolves#7191
Right now, reflection_ts_fbs target is in reflection/BUILD.bazel.
This is not ideal because reflection:reflection_fbs_schema is referenced
from :flatc in the root. Thus, for any Bazel projects that want to
include flatbuffers, they need to include npm / yarn_install and nodejs
support all because reflection/BUILD.bazel loads typescript.bzl and that
requires all TypeScript things.
This PR separated that target into a different subdirectory, freeing
root BUILD.bazel from that dependency.
Derek Bailey