Fix empty modify on JSON save or edit

[macintoshhelper]

Why does this PR exist?

Closes #2805

What does this pull request do?

• Adds a validateStudioTokensExtensions util function to strip empty studio.tokens extensions such as modify.
• Fix JSON not updating on first paste/edit by removing a useEffect dependency on getStringTokens.

Before	After

Testing this change

To reproduce

1. Go to JSON view
2. Paste this JSON:

{
 "blue": {
    "value": "#ff0000",
    "type": "color",
    "$extensions": {
      "studio.tokens": {}
    }
  },
  "red": {
    "value": "#ff0000",
    "type": "color",
    "$extensions": {
      "studio.tokens": {
        "modify": {}
      }
    }
  },
 "valid": {
    "value": "#ff0000",
    "type": "color",
    "$extensions": {
      "studio.tokens": {
        "modify": {
          "type": "darken",
          "space": "srgb",
          "value": "0.5"
        }
      }
    }
  }
}

For existing tokens with empty modify:

1. Right click and click Edit Token, then save.
2. The empty modify should be stripped.

Additional Notes (if any)

A migration step would be nice to automatically strip empty extension objects when the plugin is opened/upgraded, but this would probably be better left for a future migration system with strong testing/error catching.

[changeset-bot[bot]]

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Latest commit: a8804223ed4467a3b34e5434602285e56f03649d

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[cuserox]

✅ Tested by copy pasting the JSON, and it works!

🤔 This might not be in scope for the fix, but now that there's the validateTokensStudioExtension helper, it could be applied to other cases where these empty modify object appears. I tried replicating the issue being faced by this user(for example, the border-radius video)

With your branch locally:

• Go into renaming a token, which opens the modal and rename the token
• See the modal that asks to remap the tokens that use it
• Save it

😫 This also adds an empty modify object

My hunch is that the remapping action is adding it somewhere, maybe? REMAP_TOKENS

https://github.com/tokens-studio/figma-plugin/assets/114073780/7681da89-cfb1-4089-853d-94c5690d0a55