Highlighting emojis in Text tags is showing strange Glyphs �

**Describe the bug**

If you have emojis in Text data, highlighting them generates glyphs �

I found that if I turn off FF_LSDV_4620_3, the issue goes away:

The issue seems to be
```
self._spans = self.parent.createSpansByGlobalOffsets(self.globalOffsets);
```
https://github.com/HumanSignal/label-studio/blob/develop/web/libs/editor/src/mixins/HighlightMixin.js#L70

The spans that are generated have strange \u characters.

**To Reproduce**
Steps to reproduce the behavior:
1. Import a task with emojis
2. Make your project have a `` tag with ``.
3. Select any label, then highlight the emoji
4. see the glyph

**Expected behavior**
The emojis are properly highlighted

**Screenshots**
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**Environment (please complete the following information):**
- OS: [e.g. iOS]
- Label Studio Version [e.g. 0.8.0]

**Additional context**
Add any other context about the problem here.