Support for new corner-shape utilities (native squircle css support + more)

[quick007]

The new corner-shape utility allows developers to specify a superellipse (as well as certain supported keywords that map to superellipses, like a squircle).

It would be great to be able to use these natively in tailwind. Proposed API:

• corner-default: corner-shape: round; (not sure if round or default is a better name here)
• corner-squricle: corner-shape: squircle;
• corner-bevel: corner-shape: bevel;
• corner-scoop: corner-shape: scoop;
• corner-notch: corner-shape: notch;
• corner-square: corner-shape: sqare; (not actually sure who would use this, but good for parity)
• corner-superellipse-*: corner-shape: superellipse(number);