Tree visitors should be used to handle empty names, to do symbol filtering and to do typedef name propagation

jextract tool handles cursor/type names in many places - to filter symbols based on user options, to handle empty names (like anon. C structs), to propagate typedef names for anon structs (eg. typedef struct { int x; int y; } Point;).

It'd better to handle each of these steps by separate clang Tree visitor passes. Each concern will be localized and we can change policy in one place (if needed).