Prepare the 'svnfsfs dump-index' code for being split up into UI, FSFS internal logic and a private interface in between.
This patch introduces the interface structure but does not move any code around. We add a per index record callback function that the UI can implement to show the contents while the actual query would be run in FSFS.
* subversion/svnfsfs/dump-index-cmd.c (svn_fs_fs__dump_index_func_t): The new callback type. (dump_index_entry): The former record display part of dump_index. (svn_fs_fs__dump_index): The suggested FSFS private API function. It contains the logic of the previous dump_index but expects the FS to be passed in instead of being opened locally. Invoke the callback instead of displaying data. Finally, add cancellation support. (dump_index): Stripped down to opening the FS, writing the header line and then invoking the new function to drive the index processing.