Implement quick_symbol_functions for cooked DWARF index

Implement quick_symbol_functions for cooked DWARF index

This implements quick_symbol_functions for the cooked DWARF index.
This is the code that interfaces between the new index and the rest of
gdb.  Cooked indexes still aren't created by anything.

For the most part this is straightforward.  It shares some concepts
with the existing DWARF indices.  However, because names are stored
pre-split in the cooked index, name lookup here is necessarily
different; see expand_symtabs_matching for the gory details.