convert: give saner names to crlf/eol variables, types and functions

convert: give saner names to crlf/eol variables, types and functions

Back when the conversion was only about the end-of-line convention, it
might have made sense to call what we do upon seeing CR/LF simply an
"action", but these days the conversion routines do a lot more than just
tweaking the line ending.  Raname "action" to "crlf_action".

The function that decides what end of line conversion to use on the output
codepath was called "determine_output_conversion", as if there is no other
kind of output conversion.  Rename it to "output_eol"; it is a function
that returns what EOL convention is to be used.

A function that decides what "crlf_action" needs to be used on the input
codepath, given what conversion attribute is set to the path and global
end-of-line convention, was called "determine_action".  Rename it to
"input_crlf_action".

Signed-off-by: Junio C Hamano <gitster@pobox.com>