UX: Move user-cards above composer (#27491)

There is currently only one scenario when both the composer and a user card would be present at the same time:

if you have the composer open and then you click on something outside it that triggers a card. Which implies intent to see the card (unobstructed by the composer 😉)

The reverse doesn't happen because opening the composer would close an existing user card.

In theory there's also displaying a user card by clicking on a mention in composer's preview but that functionality is currently broken (and this PR is a prerequisite 😉)

---

I changed `.user-card, .group-card` to `.fk-d-menu[data-identifier="card"]` because that regressed when we moved user cards to float-kit – they are nested inside `.fk-d-menu` so its `z-index` is now important (effectively the cards had `z-index: z("dropdown")` instead of `z("usercard")`)

app/assets/stylesheets/common/foundation/variables.scss

@@ -95,6 +95,7 @@ $z-layers: (
   "header": 1000,
   "footer-nav": 900,
   "tooltip": 600,
+  "usercard": 500,
   "composer": (
     "dropdown": 700,
     "tooltip": 600,
@@ -102,7 +103,6 @@ $z-layers: (
     "content": 400,
   ),
   "dropdown": 300,
-  "usercard": 200,
   "timeline": 100,
   "base": 1,
 );

plugins/chat/assets/stylesheets/common/chat-drawer.scss

@@ -26,7 +26,7 @@ html.rtl {
 
 .chat-drawer-outlet-container {
   // higher than timeline, lower than composer, lower than user card (bump up below)
-  z-index: z("usercard");
+  z-index: z("composer", "content") - 1;
   position: fixed;
   right: var(--composer-right, 20px);
   left: 0;

plugins/chat/assets/stylesheets/desktop/base-desktop.scss

@@ -1,6 +1,5 @@
-.user-card,
-.group-card {
-  z-index: z("usercard") + 1; // bump up user card
+.fk-d-menu[data-identifier="card"] {
+  z-index: z("usercard");
 }
 
 .full-page-chat {