Two motivations behind this change:
1. We would like to expose the types of the Language Service to external
users (like the VSCode extension) via the npm package, on the top
level of the package
2. We would like the View Engine and Ivy LS to share a common interface
(notably after the inclusion of `getTcb`, the Ivy LS upholds a
strict superset of `ts.LanguageService`; previously both VE and Ivy
LS were aligned on `ts.LanguageService`.)
To this end, this commit refactors the exports on the toplevel of the
`language-service/` package to just be types common to both the VE and
Ivy language services. The VE and Ivy build targets then import and use
these types accordingly, and the expectation is that an external user
will just import the relevant typings from the toplevel package without
diving into either the VE or Ivy sources.
Follow up on #40607
PR Close#40621
ayazhafiz