Track newlines between paragraphs separately

Single line breaks (with no empty line) resulted in actual data loss in
the no-JS view. Only the first line was shown.

3 or more line breaks resulted in empty textareas.

All this is fixed by multiple changes:

• The text is split in a way that a paragraph can end with 1 or more newline characters.
• These newlines are part of the paragraph.
• Additionally the number of newlines is tracked as a number. This means the user can not change them in the textareas.

Bug: T202402
Change-Id: I91babeb854e3398c3cceaecff9b1f04010fa1d1a