fix: preserve text after line breaks in PowerPoint table cells

This commit addresses an issue where text after line breaks in PowerPoint table cells was lost during processing. The issue is resolved by handling cell content similarly to how it is processed for Word documents, using space separation: https://github.com/Unstructured-IO/unstructured/blob/main/unstructured/partition/docx.py#L494

unstructured/partition/pptx.py

@@ -252,7 +252,7 @@ def _iter_table_element(self, graphfrm: GraphicFrame) -> Iterator[Table]:
             return
 
         html_text = htmlify_matrix_of_cell_texts(
-            [[cell.text for cell in row.cells] for row in rows]
+            [[cell.text.replace("\n", " ") for cell in row.cells] for row in rows]
         )
         html_table = HtmlTable.from_html_text(html_text)