Derive a local's name without the keyword escape

[estebanzimanyi]

A parameter whose name is a C# keyword is escaped, so double *out reaches the
layer as @out — and the locals a body derives from it read _@out, which is
no identifier at all: the escape belongs at the start of a name or nowhere.
Every body that allocates, pins or frees around a call derives such a name, so
one function answers for all of them and the escape is dropped there.

MEOS names an out-parameter out in the four point-cloud accessors
pcpoint_get_x, _get_y, _get_z and _get_dim, and they reach the object
layer as soon as the schema they take has a class, so what the catalog answers
today does not compile. The four read _out and build.