gdb/23712: Use new multidictionary API

This patch builds on the previous by enabling the `new' multidictionary
API.  A lot of the hunks are simply textual replacements of "dict_"
with "mdict_" and similar transformations.

A word of warning, even with the use of multidictionaries, the code
still does not satisfactorily fix the reported problems with gdb/23712
(or gdb/23010). We still have additional changes to make before that
happens.

gdb/ChangeLog:

	PR gdb/23712
	PR symtab/23010
	* dictionary.h (struct dictionary): Replace declaration with
	multidictionary.
	(dict_create_hashed, dict_create_hashed_expandable)
	(dict_create_linear, dict_create_linear_expandable)
	(dict_free, dict_add_symbol, dict_add_pending, dict_empty)
	(dict_iterator_first, dict_iterator_next, dict_iter_match_first)
	(dict_iter_match_next, dict_size): Rename to "mdict_" versions
	taking multidictionary argument.
	[ALL_DICT_SYMBOLS]: Update for multidictionary.
	* block.h (struct block) <dict>: Change to multidictionary
	and rename `multidict'.
	* block.c, buildsym.c, jit.c, mdebugread.c, objfiles.c,
	symmisc.c: Update all dictionary references to multidictionary.