feat: add FeMerge and FeMergeNode filters

[jakex7]

Summary

As mentioned in #2362
Introduce new filters:

• FeMerge
• FeMergeNode

Example usage

<Svg width="200" height="200">
  <Filter id="mergeWithOffset" width="180" height="180">
    <FeOffset dx="50" dy="50" result="test" />
    <FeOffset dx="100" dy="100" in="SourceGraphic" />
    <FeMerge>
      <FeMergeNode in="SourceGraphic" />
      <FeMergeNode in="test" />
      <FeMergeNode />
    </FeMerge>
  </Filter>
  <Rect
    x="0"
    y="0"
    width="100"
    height="100"
    stroke="black"
    fill="red"
    filter="url(#mergeWithOffset)"
  />
</Svg>

Test Plan

Example app -> Filters -> FeMerge

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

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