Make SingleLineJsonParser read log lines with line feed and handle JSON parser exception

[dhhoang]

Description

This PR fixes several issues regarding SingleLineJsonParser:

• Currently, if there is a log record that is invalid JSON, the parser is not able to handle the parsing Exception and DirectorySource is not able to update the log file's position. As a result, the agent will keep reading the same record and failling over and over again. This PR catches the Exception, log the error message, and skip the invalid record.
• Some customers write log records larger than NLog's buffer size (1024), and so a record line may not be written completely at once. (e.g. NLog writes {"key": first, then write the rest "value"} after a while. When that happens, Kinesis agent thinks that {"key": is the entire record and fails, because the SingleLineJsonParser uses StreamReader.ReadLine(), which returns a string when EndOfStream is reached EVEN IF there is no new line sequence. This PR adds a new class FileLineReader, which returns a line ONLY IF it ends with a new line sequence. This allows SingleLineJsonParser to always parse the complete JSON record line.

Testing

Added 2 new sets of tests: FileLineReaderTest to test the behavior of FileLineReader, and SingleLineJsonParserTest to test the behavior of SingleLineJsonParser using the new ReadLine functionality.