Update grammar with @unstable and @since annotations

[ricochet]

The pull request #332 to the WebAssembly component model introduces @unstable and @since gates to the WebAssembly Interface Type (WIT) IDL. These gates aim to simplify version updates by annotating new features with the version they were introduced in, reducing the need for multiple document snapshots.

Example WIT definition:
https://github.com/WebAssembly/WASI/blob/29c4c11f417335c8a0378608795ef83c80d4293b/preview2/cli/environment.wit

[github-actions]

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[github-actions]

🎉 This change has been included in wit-idl-v0.3.4 🎉

The release is available on:

• GitHub releases: wit-idl: v0.3.4

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