Ensure that block types get represented correctly in declaration
fragments, as block parameter names are important for documentation
clients we need a separate system from getFragmentsForType in order to
have access to full ParmVarDecls for the parameters.
rdar://118257401
Other implementations of the symbol graph format use zero-based indices
for source locations, which causes problems when combined with clang's
current one-based indices. This commit sets ExtractAPI's symbol graph
output to use zero-based indices to align with other implementations.
rdar://107639783
