Regression in tests from [0] tests were written to assume a newline was
added to the result of Text.as_string which is no longer the case.
[0]: f4ff36431ccfac2f0a99fc23c18fe0d9de38b36d
Add the ability to get/set the selected text.
**Calling the new methods:**
- `bpy.data.texts["Text"].region_as_string()`
- `bpy.data.texts["Text"].region_from_string("Replacement")`