feat: Render diffs in email notifications (#4164)

* deps

* diffCompact

* Diffs in email

* test

* fix: Fade deleted images
fix: Don't include empty paragraphs as context
fix: Allow for same image multiple times and refactor

* Remove target _blank

* fix: Table heading incorrect color

server/models/helpers/DocumentHelper.test.ts

@@ -0,0 +1,83 @@
+import Revision from "@server/models/Revision";
+import DocumentHelper from "./DocumentHelper";
+
+describe("toEmailDiff", () => {
+  test("toEmailDiff", () => {
+    const before = new Revision({
+      title: "Title",
+      text: `
+This is a test paragraph
+
+- list item 1
+- list item 2
+
+:::info
+Content in an info block
+:::
+
+!!This is a placeholder!!
+
+==this is a highlight==
+
+- [ ] checklist item 1
+- [ ] checklist item 2
+- [x] checklist item 3
+
+same on both sides
+
+same on both sides
+
+same on both sides`,
+    });
+
+    const after = new Revision({
+      title: "Title",
+      text: `
+This is a test paragraph
+
+A new paragraph
+
+- list item 1
+
+This is a new paragraph.
+
+!!This is a placeholder!!
+
+==this is a highlight==
+
+- [x] checklist item 1
+- [x] checklist item 2
+- [ ] checklist item 3
+- [ ] checklist item 4
+- [x] checklist item 5
+
+same on both sides
+
+same on both sides
+
+same on both sides`,
+    });
+
+    const html = DocumentHelper.toEmailDiff(before, after);
+
+    // marks breaks in diff
+    expect(html).toContain("diff-context-break");
+
+    // changed list
+    expect(html).toContain("checklist item 1");
+    expect(html).toContain("checklist item 5");
+
+    // added
+    expect(html).toContain("A new paragraph");
+
+    // Retained for context above added paragraph
+    expect(html).toContain("This is a test paragraph");
+
+    // removed
+    expect(html).toContain("Content in an info block");
+
+    // unchanged
+    expect(html).not.toContain("same on both sides");
+    expect(html).not.toContain("this is a highlight");
+  });
+});