[libtooling] support CXXFunctionalCastExpr

Summary: Support CXXFunctionalCastExpr

Test Plan:
DEBUG=1 make -C libtooling clean all
make -C libtooling clean test
make -C clang-ocaml clean
make -C clang-ocaml test

Reviewers: mathieubaudet

Reviewed By: mathieubaudet

Subscribers: martinoluca

Differential Revision: https://phabricator.fb.com/D1428817

Tasks: 3964417