Fix row_count always being 1 when \r used as lineTerminator

[kspurgin]

This PR fixes the fact that row_count was always reported as 1 for CSVs using \r as lineTerminator, even if the dialect explicitly set lineTerminator to \r.

The cause of this issue was the use of #each_line method to split streams/files into lines sent to #parse_line. With no arguments given, #each_linereads lines as determined by line separator $/.¹ By default, $/ is set to \n.²

This results in the entire stream/file being sent to #parse_line, which was explicitly only treating \n as a line break.

This was fixed by:

1. Making all places that checked for line breaks by matching only on \n check for either \n or \r

2. Deriving the correct $/ value prior to calling #each_line, and then resetting $/ to the default value after the #each_line block is closed.

The latter is currently accomplished by:

• Using the dialect lineTerminator value if set to an actual String value (e.g. not :auto)
• Otherwise, get the entire @source as a String. If this includes \n, set $/ to \n. Otherwise, set it to \r

The second step has 2 problems:

• Performance on gigantic files
• Potential to blow up or cause other problems if a quoted field value contains \n or \r\n, but the file's actual lineTerminator is \r

I am going ahead with this implementation for now because:

• Our use case generally should not involve CSV so large that the first is an issue
• The second just opens up an abyss of pain for a somewhat unlikely use case that isn't working correctly prior to this change, either

I have an idea for an approach that would address both of those issues, but it gets me halfway to writing a CSV parser from scratch and I ain't got time for that at the moment.

Footnotes

1. https://docs.ruby-lang.org/en/master/IO.html#method-i-each_line ↩

2. https://docs.ruby-lang.org/en/master/globals_rdoc.html#label-24-2F+-28Input+Record+Separator-29 ↩