chore(typescript_indexer): TypeScript 3.6 compat. (#4185)
chore(typescript_indexer): TypeScript 3.6 compat. (#4185)

This introduces a backwards compatible shim for
ts.isParameterPropertyDeclaration that works in TS3.5 & TS3.6.

This shim can be inlined (and thus removed) once Kythe can fully move to
TypeScript 3.6.
kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe