feat(vcs): Accept a diff change from the keyboard and step between diff files (#158)

- Accept Left Side / Accept Right Side copy the change at the caret to the
  other side of a side-by-side diff (⌃⌘→ / ⌃⌘← on macOS, Ctrl+Alt+R /
  Ctrl+Alt+A on Windows).
- Compare Next File / Compare Previous File open the neighbouring file of
  the diff chain directly (⌃⇧→ / ⌃⇧← on macOS, Alt+Shift+→ / ← on Windows).

src/features/settings/__tests__/downloadJdk.test.tsx

@@ -66,6 +66,7 @@ describe("Download JDK dialog", () => {
   it("preselects the version a fix asks for", async () => {
     render(<DownloadJdkDialog initialVersion={21} onClose={() => {}} onDownloaded={() => {}} />);
     await waitFor(() => expect(screen.getByRole("button", { name: "Download" })).toBeEnabled());
-    expect(screen.getByRole("button", { name: "Version" })).toHaveTextContent("21");
+    // The version list loads after the Download button enables on a busy runner.
+    await waitFor(() => expect(screen.getByRole("button", { name: "Version" })).toHaveTextContent("21"));
   });
 });