Merge branch 'mt/parallel-checkout-part-1'

Preparatory API changes for parallel checkout. * mt/parallel-checkout-part-1: entry: add checkout_entry_ca() taking preloaded conv_attrs entry: move conv_attrs lookup up to checkout_entry() entry: extract update_ce_after_write() from write_entry() entry: make fstat_output() and read_blob_entry() public entry: extract a header file for entry.c functions convert: add classification for conv_attrs struct convert: add get_stream_filter_ca() variant convert: add [async_]convert_to_working_tree_ca() variants convert: make convert_attrs() and convert structs public