Improve TSV serialization for tab and newline characters in cell value when copying cells to the clipboard

[seancolsen]

Current behavior

• You can copy the selected cells in a sheet via Ctrl+C (Cmd+C on Mac OS).

• Mathesar writes one string to the clipboard, a TSV representation of the cells.

• The TSV serialization logic is very simplistic. Columns are separated by tab characters. Rows are separated by newline characters.

• If a cell value contains a tab or newline character, the TSV serialization will not accurately represent the cell values.

  You can test this out by setting a cell value to some text which contains a newline. Either use Ctrl+Enter to manually enter a newline, or paste some text into the cell which contains a newline. When rendering the cell in select mode, the newline won't display. It will show again when you enter edit mode on the cell though.

  Here I have four cells, and I have newlines entered between "apple" and "banana" and also between "broccoli" and "carrot"

  

  Copying the cells gives this text:

  apple
  banana	cherry
  asparagus	broccoli
  carrot
  

  If you paste that text into another spreadsheet application, you'll get six cells instead of four. That's not good

Desired behavior

• Our Clipboard Interaction specs has a TSV section with more details about how the serialization logic should work.

• In the above example, copying those four cells should give this text:

  "apple
  banana"	cherry
  asparagus	"broccoli
  carrot"
  

  The double quotes ensure that the newlines are parsed as cell content rather than row delimiters.

Implementation

• We also need to deserialize the TSV string during paste, and that logic is more complex. As such, we should see if we can find a 3rd party library to handle the serialization and deserialization for us.

[seancolsen]

Note: we also need to properly handle commas and quotes in cell contents too