TextView: Select dropped text if focused

This is convenient and used in most text editors.

Change-Id: Ia39b9e6f16cc381a62e10b248033729179a0996c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2110
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: John Scipione <jscipione@gmail.com>
Reviewed-by: Niels Sascha Reedijk <niels.reedijk@gmail.com>

src/kits/interface/TextView.cpp

@@ -4915,6 +4915,8 @@ BTextView::_MessageDropped(BMessage* message, BPoint where, BPoint offset)
 		}
 
 		Insert(dropOffset, text, dataLength, runArray);
+		if (IsFocus())
+			Select(dropOffset, dropOffset + dataLength);
 	}
 
 	return true;