Locates a paragraph boundary in @text.
A boundary is caused by delimiter characters, such as a newline, carriage return, carriage return-newline pair, or Unicode paragraph separator character.
The index of the run of delimiters is returned in @paragraph_delimiter_index. The index of the start of the next paragraph (index after all delimiters) is stored n @next_paragraph_start.
If no delimiters are found, both @paragraph_delimiter_index and @next_paragraph_start are filled with the length of @text (an index one off the end).
length of @text in bytes, or -1 if nul-terminated
return location for index of delimiter
return location for start of next paragraph