Block Bindings: Add postType to context for Post Data source

[ockham]

The Post Data source is currently only providing postId providing, but not postType context, even though the client side requires the latter. Since that requirement is not met, the source doesn't work quite properly in the editor. (Among other things, it shows up as read-only in the editor.)

Found while testing WordPress/gutenberg#71542.

Trac ticket: https://core.trac.wordpress.org/ticket/63994

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

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Props bernhard-reiter.

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[cbravobernal]

LGTM

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 60778
GitHub commit: d64970a

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.

[cbravobernal]

Committed in https://core.trac.wordpress.org/changeset/60778