glossary link for ‘obviously typed’ in obvious * types docs

[IldySilva]

fix 6993
fix 6994
fix 6992

This PR adds a hyperlink from “obvious” / “obviously typed” to the official glossary entry: https://dart.dev/resources/glossary#obviously-typed.

[copybara-service]

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[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/466620 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/466620 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/466620 has been updated with the latest commits from this pull request.

[copybara-service]

https://dart-review.googlesource.com/c/sdk/+/466620 has been updated with the latest commits from this pull request.