Option for fixed text length

As per a user request, it might be useful to have an option to specify a specific text length, instead of the text adjusting to the text area size.

Proposed implementation

The behavior would be the same as before for point text, i.e., two words would get used.

The dialog would get another option, text length. Implemented as radio buttons, this gives the user two choices:

Text length:

Also, a slider gets added to specify the text length. This would be disabled when "Adjust to layer" is selected.

A first, rough estimation for this implementation would be 2 hours.