This reuses the stringform concept and introduces a similar bodyform
flag for STRINGS and BLOB types. We can now assign either a STRING or
a BLOB to [be]resp.body, without breaking the VRT ABI and API. In fact,
the VRT API now uses a void* C type for the BODY VCL type and finds
which type to use based on enum lbody_e.

The enum completely changed but macros were added to maintain the API,
and because of this change, enum lbody_e literals are formatted in two
steps. As a result the BODY type grew another noindent flag. It prevents
the insertion of white space between the LBODY_{ADD,SET}_ prefix and the
type name suffix (BLOB or STRANDS).