feat: additional stylesheet for SvgCss

[jakex7]

Summary

resolves #1841

Test Plan

import * as React from 'react';
import {SvgCss} from 'react-native-svg/css';

const Icon = () => (
  <SvgCss
    xml={`
      <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
        <style>.secondary{opacity:.4}</style>
        <g id="root">
          <path id="primary" d="M256 512C114.6 512 0 397.4 0 256C0 114.6 114.6 0 256 0V512z"/>
          <path class="secondary" d="M256 0C397.4 0 512 114.6 512 256C512 397.4 397.4 512 256 512V0z"/>
        </g>
      </svg>`}
    // =================================== String ===================================
    stylesheet={`
      #root {
        color: #0f0;
      }
      #primary {
        fill: #f00;
      }
      .secondary {
        fill: currentColor;
      }
    `}
    // =================================== Object ===================================
    stylesheet={{
      '#root': {
        fill: '#f00',
      },
      '#primary': {
        fill: '#f00',
      },
      '.secondary': {
        fill: 'currentColor',
      },
    }}
  />
);
export default Icon;

Checklist

• I have tested this on a device and a simulator
• I added documentation in README.md
• I updated the typed files (typescript)
• I added a test for the API in the __tests__ folder