Polish tagged template literals

[tsnobip]

Allow modules in tagged template literals

Allow to write this:

let taggedTemplate = Pg.sql`select * from ${table} where id = ${id}`

Fix reexport tagged template externals

Without this fix, when reexporting tagged template external bindings, it would raise

File "jscomp/core/lam_compile_external_call.ml", line 262, characters 17-23: Assertion failed

[zth]

Awesome! Just one small comment as you can see.