feat: improved serialization of the rotate property

[yisibl]

This PR refactors the serialization of the rotate property value according to the CSS Transforms 2 specification.

Previously, rotate: 0deg was incorrectly serialized as rotate: none. The specification clearly states that rotate: 0deg creates a stacking context and containing block, while rotate: none does not.

See Demo: https://codepen.io/yisi/pen/QwEJEmr?editors=0100

All three properties accept (and default to) the value none, which produces no transform at all. In particular, this value does not trigger the creation of a stacking context or containing block for all descendants, while all other values (including “identity” transforms like translate: 0px) create a stacking context and containing block for all descendants, per usual for transforms.
https://drafts.csswg.org/css-transforms-2/#valdef-translate-none

This PR fixes this issue and also provides additional compression benefits.

• minify_test(".foo { rotate: -0deg }", ".foo{rotate:0deg}");
• minify_test(".foo { rotate: z 10deg }", ".foo{rotate:10deg}");
• minify_test(".foo { rotate: 0 0 1 10deg }", ".foo{rotate:10deg}");
• minify_test(".foo { rotate: 10deg 0 0 -1 }", ".foo{rotate:-10deg}");

Fixes: #1136