web: Localise fullscreen toggle

web/packages/core/src/ruffle-player.ts

@@ -1218,12 +1218,12 @@ export class RufflePlayer extends HTMLElement {
         if (this.fullscreenEnabled) {
             if (this.isFullscreen) {
                 items.push({
-                    text: "Exit fullscreen",
+                    text: text("context-menu-exit-fullscreen"),
                     onClick: () => this.instance?.set_fullscreen(false),
                 });
             } else {
                 items.push({
-                    text: "Enter fullscreen",
+                    text: text("context-menu-enter-fullscreen"),
                     onClick: () => this.instance?.set_fullscreen(true),
                 });
             }

web/packages/core/texts/en-US/context_menu.ftl

@@ -7,3 +7,5 @@ context-menu-about-ruffle =
         *[other] About Ruffle ({$version})
     }
 context-menu-hide = Hide this menu
+context-menu-exit-fullscreen = Exit fullscreen
+context-menu-enter-fullscreen = Enter fullscreen