Editor: Expose the embed core block on the server.

Props ntsekouras, gziolo.
Fixes #51531.
Built from https://develop.svn.wordpress.org/trunk@49210


git-svn-id: http://core.svn.wordpress.org/trunk@48972 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/blocks/embed/block.json

@@ -0,0 +1,37 @@
+{
+	"name": "core/embed",
+	"category": "embed",
+	"attributes": {
+		"url": {
+			"type": "string"
+		},
+		"caption": {
+			"type": "string",
+			"source": "html",
+			"selector": "figcaption"
+		},
+		"type": {
+			"type": "string"
+		},
+		"providerNameSlug": {
+			"type": "string"
+		},
+		"allowResponsive": {
+			"type": "boolean",
+			"default": true
+		},
+		"responsive": {
+			"type": "boolean",
+			"default": false
+		},
+		"previewable": {
+			"type": "boolean",
+			"default": true
+		}
+	},
+	"supports": {
+		"align": true,
+		"reusable": false,
+		"html": false
+	}
+}