Correct newline-style in json emitter

[davidBar-On]

Suggested fix for issue #4273 - using the configured newline_style for the emitted JSON expected parts. The PR is based on back-porting PR #4743 (that was not merged into R2).

The approach taken is to propagate the newline-style setting by adding emit_formatted_file_with_line_style() function to the Emitter trait, and changing the default emit_formatted_file() to call it. All emit_formatted_file implementation were changed to emit_formatted_file_with_line_style, but the relevant code still calls emit_formatted_file. This is except for the JsonEmitter that calls emit_formatted_file_with_line_style directly with the newline-style setting, and the function is using it for the emitted expected parts.

Based on a comment to PR #4743, testings were added to writemode, to allow using test files.