Add multiline appearance and rows attribute for text inputs

[lognaturel]

The rows attribute specifies the number of rows a textbox should take initially:

• ODK XForms spec: https://getodk.github.io/xforms-spec/#body-attributes
• User-facing docs: https://docs.getodk.org/form-question-types/#id44

In Collect, the field expands vertically as needed. In Enketo, there's a vertical scrollbar if needed.

Enketo also has a multiline appearance for text fields which is equivalent to N rows. We should pick a number of rows and then match that in Collect (getodk/collect#6337).