Add an alternative pin icon (#17411)

We'll use this for the pinned tabs feature.

---

Release Notes:

- N/A

crates/ui/src/components/icon.rs

@@ -213,6 +213,7 @@ pub enum IconName {
     Pencil,
     Person,
     Pin,
+    PinAlt,
     Play,
     Plus,
     PocketKnife,
@@ -385,6 +386,7 @@ impl IconName {
             IconName::Pencil => "icons/pencil.svg",
             IconName::Person => "icons/person.svg",
             IconName::Pin => "icons/pin.svg",
+            IconName::PinAlt => "icons/pin_alt.svg",
             IconName::Play => "icons/play.svg",
             IconName::Plus => "icons/plus.svg",
             IconName::PocketKnife => "icons/pocket_knife.svg",