Editor: Expose the `embed` core block on the server.

Props ntsekouras, gziolo.
Fixes #51531.

git-svn-id: https://develop.svn.wordpress.org/trunk@49210 602fd350-edb4-49c9-b593-d223f7449a82

src/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
+	}
+}

src/wp-includes/blocks/index.php

@@ -33,6 +33,7 @@ function register_core_block_types_from_metadata() {
 		'code',
 		'column',
 		'columns',
+		'embed',
 		'file',
 		'gallery',
 		'group',

tools/webpack/packages.js

@@ -123,6 +123,7 @@ module.exports = function( env = { environment: 'production', watch: false, buil
 		'code',
 		'column',
 		'columns',
+		'embed',
 		'file',
 		'gallery',
 		'group',