[libTooling] Fix r374962: add more Transformer forwarding decls.

Summary:
The move to a new, single namespace in r374962 left out some type definitions
from the old namespace and resulted in one naming conflict (`text`).  This
revision adds aliases for those definitions and removes one of the `text`
functions from the new namespace.

Reviewers: alexfh

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69036

llvm-svn: 375003