The textbox with auto width based on the value can be obtained as follows:
1) Insert an expression box into your form
2) Set the field you want to display in this text box
3) Right-Click on expression box => Expression box Properties... => Display
4) Uncheck "Wrap Text" option
5) Go to Size tab => Remove the value in the Width
6) Click Apply
7) Publish the form and test the output.