[llvm] [bazel] Add td_library target for OptParser.td (PR #86363)

[Keith Smiley via llvm-commits]

keith wrote:

> Do you know what the difference is w/ your downstream use case that including that file directly doesn't work?

The issue is the downstream library doesn't have the right include paths when just importing the file vs the library which propagates its directory

https://github.com/llvm/llvm-project/pull/86363