Add option to don't show keyboard when input is focused

[castanonrodrigo]

Hey guys, I've made this PR so we are able to choose if the keyboard should appear or not.
I noticed that in some use cases we have few options to choose from and the device's keyboard takes up to much of the screen, making it hard to use the suggestions box properly.
Please let me know if you have any feedback, thanks!

[codecov-io]

Codecov Report

Merging #78 (5cfcfae) into master (8c08caa) will decrease coverage by 0.28%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #78      +/-   ##
==========================================
- Coverage   35.12%   34.83%   -0.29%     
==========================================
  Files           3        3              
  Lines         242      244       +2     
==========================================
  Hits           85       85              
- Misses        157      159       +2     

Impacted Files	Coverage Δ
lib/src/chips_input.dart	31.10% <0.00%> (-0.31%)	⬇️

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[awhitford]

Are you still trying to keep the control editable -- but just trying to hide the keyboard because the user has an external keyboard? Or is this hiding the keyboard strategy designed for non-editable Chips Input?

The decision to hide or show the keyboard strikes me as something that the OS should take care of doing -- not the app or widget. The OS knows if there is an external keyboard. The OS also has different keyboard options. If one chooses at the widget level to hide the keyboard and the user is using a tablet with no external keyboard, what is expected to happen?

[castanonrodrigo]

It's designed for non-editable Chips Input.
The goal is to make an input that is similiar to a default flutter dropdown, but can receive multiple entries instead of just one. So it wouldn't be possible to search for options or edit chips in this use case.