Add: Template types to the patterns API.
Backports https://github.com/WordPress/gutenberg/pull/45814 into the core.
This commit adds a new templateType property to the patterns registration API.
This property allows a pattern to specify which template it makes sense on, e.g.: 404, single-post, single-product, category.
Props youknowriad, ntsekouras,
spacedmonkey.
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