[TS/Bazel] Minor improvements to typescript.bzl

[jkuszmaul]

• Uses @...// dependencies so that flatbuffers can actually be used as an external repo (had forgotten to upstream this earlier).
• Allows using flatbuffer_ts_library to generate reflection schemas in the same way that flatbuffer_cc_library does (but default it to off to avoid behavioral changes).
• Pass through a package_name attribute to flatbuffer_ts_library to allow non-relative imports of generated typescript code.
• Fix bazel build regression caused by #7342, re-implementing #7342.

[jkuszmaul]

@dbaileychess not sure who to ask for review on this (also the android build is looking flaky?).

cc @AustinSchuh as the last known maintainer for flatbuffers bazel rules...

[dbaileychess]

@AustinSchuh Could you take a look?

[liuliu]

Thank you for the fix!

[jkuszmaul]

@dbaileychess ping