Add viewport-aware max-height constraints and Material 3 scrollbar styling to Menu

- Update core Menu stylesheet (menu.scss) to set max-height: calc(100vh - 100px) on popover host and max-height: inherit on .menu.menu-host
- Add Material 3 floating pill scrollbar styles (6px rounded thumb, transparent track) to core Menu container

PiperOrigin-RevId: 970083346

Author: material-web-copybara

labs/gb/components/menu/menu.scss

@@ -33,18 +33,40 @@
 
     &:popover-open,
     :host(:popover-open):has(&.menu-host) {
-      position-area: end span-end;
       border: none;
+      max-height: calc(100vh - 100px);
+      position-area: end span-end;
     }
 
     :host(:popover-open):has(&.menu-host) {
-      overflow: visible;
       background: none;
+      max-height: calc(100vh - 100px);
+      overflow: visible;
       padding: 0;
     }
 
     &.menu-host {
+      max-height: inherit;
       overflow: auto;
+      scrollbar-color: var(--md-sys-color-outline-variant) transparent;
+      scrollbar-width: thin;
+
+      &::-webkit-scrollbar {
+        width: 6px;
+      }
+
+      &::-webkit-scrollbar-track {
+        background: transparent;
+      }
+
+      &::-webkit-scrollbar-thumb {
+        background-color: var(--md-sys-color-outline-variant);
+        border-radius: 9999px;
+      }
+
+      &::-webkit-scrollbar-thumb:hover {
+        background-color: var(--md-sys-color-outline);
+      }
     }
 
     .divider,