add last_row in get_text_from_semantic_region

[mgpinf]

This commit adds the last row into account while computing the pane:get_text_from_semantic_region(zone) method.

This fixes the following:

• #5806
• #5346

I have tested the code, and the last line of semantic zone is now part of the result.

Just want to confirm that this does not conflict with anything