This change adds a `--recognizer-function` (`-R`) to `type summary add`
and `type synth add` that allows users to specify that the names in
the command are not type names but python function names.
It also adds an example to lldb/examples, and a section in the data
formatters documentation on how to use recognizer functions.
Differential Revision: https://reviews.llvm.org/D137000
Jorge Gorbe Moya