feat: support css variables for SvgCss (#2459)

# Summary
Feature #2380 

We want to add support for CSS variables when passing them to parse the
SVG XML source function.

## Test Plan
Test app -> src -> Test2380

## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ✅     		 |
| MacOS   |    ✅        |
| Android |    ✅     	|
| Web     |    ✅		    |

---------

Co-authored-by: Jakub Grzywacz <jakub.grzywacz@swmansion.com>

apps/test-examples/index.tsx

@@ -27,6 +27,7 @@ import Test2327 from './src/Test2327';
 import Test2233 from './src/Test2233';
 import Test2363 from './src/Test2363';
 import Test2366 from './src/Test2366';
+import Test2380 from './src/Test2380';
 import Test2397 from './src/Test2397';
 import Test2403 from './src/Test2403';
 import Test2407 from './src/Test2407';

apps/test-examples/src/Test2380.tsx

@@ -0,0 +1,58 @@
+import React from 'react';
+import {View} from 'react-native';
+import {SvgCss} from 'react-native-svg/css';
+
+const xml = `
+<svg width="200" height="200" id="mySVG" viewBox="0 0 200 200">
+    <style>
+      #mySVG {
+        --my-color: #ff0000;
+        --color: #3e3efe;
+        --green-color: green;
+        --my-gold-stop-color: gold;
+        --my-red-stop-color: red;
+        --my-feFlood-color: green;
+      }
+      #newId {
+        fill: purple;
+        }
+    </style>
+    <defs>
+    <linearGradient id="myGradient">
+      <stop offset="5%" stop-color="var(--my-gold-stop-color)" />
+      <stop offset="95%" stop-color="var(--my-red-stop-color)" />
+    </linearGradient>
+    <filter id="spotlight">
+      <feFlood
+        result="floodFill"
+        x="0"
+        y="0"
+        width="100%"
+        height="100%"
+        flood-color="var(--my-feFlood-color)"
+        flood-opacity="1" />
+      <feBlend in="SourceGraphic" in2="floodFill" mode="multiply" />
+    </filter>
+    </defs>
+    <rect fill="var(--color)" x="40" y="40" width="32" height="32" />
+    <rect id="newId" x="80" y="40" width="32" height="32" />
+    <text fill="var(--color)" x="20" y="100" stroke="var(--green-color)" stroke-width="1" font-size="16">Hello</text>
+    <circle cx="140" cy="55" r="15" fill="url(#myGradient)" />
+
+    <image
+      href="https://static-00.iconduck.com/assets.00/mdn-icon-2048x1806-enhibj42.png"
+      x="0"
+      y="40"
+      width="32"
+      height="32"
+      style="filter:url(#spotlight);" />
+  </svg>
+`;
+
+export default function SvgComponent() {
+  return (
+    <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
+      <SvgCss xml={xml} height="200" width="200" />
+    </View>
+  );
+}