Define JSI bridging function for ShadowNode::Shared

[rubennorte]

Summary: Changelog: [internal]

This defines a new bridging method to convert ShadowNode::Shared from and to JS. This has some benefits over the existing shadowNodeFromValue and valueFromShadowNode functions:

1. It's more convenient, as we can just use ShadowNode::Shared in classes implementing the codegen, and the runtime will do the conversion automatically.
2. It's safer, as it checks for nullability and throws JS exceptions except of having segmentation faults down the line.

Differential Revision: D75597542

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This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75597542

[facebook-github-bot]

This pull request has been merged in facebook/react-native@9c2148920c1c679f3ece295bc4614e9af7854a63.

[react-native-bot]

This pull request was successfully merged by @rubennorte in 9c2148920c1c679f3ece295bc4614e9af7854a63

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