Increase input font-size to 16px on mobile

[broccolini]

This pr fixes https://github.com/github/design-systems/issues/405

It gives the input field a font-size of 16px on mobile from the md breakpoint and up it will have 14px, this means inputs won't zoom in on mobile on responsive pages.

To do:

• test in github/github
  • mobile
  • tablet
  • desktop

cc @primer/design-systems @kevinsawicki

[kevinsawicki]

Looks good to me 👍

[broccolini]

Despite what the status check says, the alpha version is 10.3.0-alpha.9c5fbfd8

[broccolini]

Tested in review-lab https://input-size.review-lab.github.com/

• Doesn't seem to cause any unwanted behavoir on dotcom. If you reduce your screensize to a super narrow window the font-size will increase but doesn't effect the size of the input field so it doesn't cause any problems with layout.
• It was difficult to test a real scenario on iPad and mobile without a new responsive layout, however it didn't cause any problems with the current site on dotcom product and site pages.