Add support for Grist embeds. (#3914)

* Add support for Grist embeds.

* Change Grist integration to only support SaaS

* Update Regex

* Update shared/editor/embeds/index.tsx

Co-authored-by: Apoorv Mishra <apoorvmishra101092@gmail.com>

* Change Grist embed to use function based API

* Convert standard URL into embed url

* Update shared/editor/embeds/Grist.tsx

Co-authored-by: Apoorv Mishra <apoorvmishra101092@gmail.com>

* Update shared/editor/embeds/Grist.tsx

Co-authored-by: Apoorv Mishra <apoorvmishra101092@gmail.com>

* Update shared/editor/embeds/Grist.tsx

Co-authored-by: Apoorv Mishra <apoorvmishra101092@gmail.com>

* Lint and test updates

Co-authored-by: Apoorv Mishra <apoorvmishra101092@gmail.com>
Co-authored-by: Tom Moor <tom.moor@gmail.com>

shared/editor/embeds/Grist.tsx

@@ -0,0 +1,27 @@
+import * as React from "react";
+import Frame from "../components/Frame";
+import Image from "../components/Image";
+import { EmbedProps as Props } from ".";
+
+function Grist(props: Props) {
+  return (
+    <Frame
+      {...props}
+      src={props.attrs.href.replace(/(\?embed=true)?$/, "?embed=true")}
+      icon={
+        <Image
+          src="/images/grist.png"
+          alt="Grist Icon"
+          width={16}
+          height={16}
+        />
+      }
+      title="Grist Spreadsheet"
+      border
+    />
+  );
+}
+
+Grist.ENABLED = [new RegExp("^https?://([a-z.-]+\\.)?getgrist\\.com/(.+)$")];
+
+export default Grist;