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ARROW-7368: [Ruby] Use :arrow_file and :arrow_streaming for format name

:batch isn't suitable because we use "Apache Arrow IPC File Format" as
format name.

:stream is ambiguous.

Closes #6009 from kou/ruby-table-load-arrow-format-name and squashes the following commits:

4502bf59a <Sutou Kouhei>  Use :arrow_file and :arrow_streaming for format name

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>