feat: add textLength prop to TextPath TSpan

[bohdanprog]

trafficstars

Summary

Motivation: We want to add that feature. Closes #1767

example with TextPath component

Test Plan

The example is available in the test-examples app as Test1693

What are the steps to reproduce (after prerequisites)?

Compatibility

OS	Implemented
iOS	✅
Android	✅
Web	✅
MacOS	✅

[jakex7]

Great, but it still doesn't seem to work on either Text or TextPath

<Svg viewBox="0 0 200 200">
  <Path d="M 50, 100 a 50,50 0 1,0 100,0 a 50,50 0 1,0 -100,0 Z" fill="red"/>
  <Path d="M 50, 100 a 50,50 0 1,0 100,0 a 50,50 0 1,0 -100,0 Z" fill="red" id="path"/>
  <Text fill="blue" textLength="314">
    <TextPath href="#path">
      We go up and down,
      <TSpan fill="green">
        then up again
      </TSpan>
    </TextPath>
  </Text>
</Svg>

In the example above it only works when textLength is set on TSpan

EDIT: It doesn't matter if textLength is set to Text or TextPath.