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