Bump @babel/plugin-proposal-decorators from 7.10.5 to 7.12.1 (#15008)

Bump @babel/plugin-proposal-decorators from 7.10.5 to 7.12.1 (#15008)

Bumps [@babel/plugin-proposal-decorators](https://github.com/babel/babel/tree/HEAD/packages/babel-plugin-proposal-decorators) from 7.10.5 to 7.12.1.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/main/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.12.1/packages/babel-plugin-proposal-decorators)

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