Allow main menu modals to be closed by clicking escape (#1617)

## Description:



Allow the main menu modals to be closed by clicking the Escape key. The
manner by which this change achieves this is by adding a
connectedCallback to add a keydown EventListener, which closes the modal
on clicking Escape.

Relevant issue: #1586 

My earlier PR was only for the in-game modals, as they can access the
Event Bus and receive the CloseViewEvent.
https://github.com/openfrontio/OpenFrontIO/pull/1604

As mentioned, this PR differs in that it does not use the Event Bus
because these are not in-game modals. The main menu modals do not have
access to the event bus.

Affected modals for this PR.
- UserSettingModal.ts
- TerritoryPatternsModal.ts
- SingePlayerModal.ts
- NewsModal.ts
- LanguageModal.ts
- JoinPrivateLobbyModal.ts
- HostLobbyModal.ts
- HelpModal.ts
- FlatInput.ts








## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA agreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

slyty

---------

Co-authored-by: Antoine <antoine.gannat@gmail.com>

src/client/HelpModal.ts

@@ -15,6 +15,23 @@ export class HelpModal extends LitElement {
     return this;
   }
 
+  connectedCallback() {
+    super.connectedCallback();
+    window.addEventListener("keydown", this.handleKeyDown);
+  }
+
+  disconnectedCallback() {
+    window.removeEventListener("keydown", this.handleKeyDown);
+    super.disconnectedCallback();
+  }
+
+  private handleKeyDown = (e: KeyboardEvent) => {
+    if (e.code === "Escape") {
+      e.preventDefault();
+      this.close();
+    }
+  };
+
   render() {
     return html`
       <o-modal