assistant: Add action footer and refine slash command popover (#16360)

- [x] Put the slash command popover on the footer
- [x] Refine the popover (change it to a picker)
- [x] Add more options dropdown on the assistant's toolbar
- [x] Add quote selection button on the footer

---

Release Notes:

- N/A

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>
Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Kirill Bulatov <mail4score@gmail.com>

crates/ui/src/components/icon.rs

@@ -157,6 +157,7 @@ pub enum IconName {
     Disconnected,
     Download,
     Ellipsis,
+    EllipsisVertical,
     Envelope,
     Escape,
     ExclamationTriangle,
@@ -233,6 +234,8 @@ pub enum IconName {
     Server,
     Settings,
     Shift,
+    Slash,
+    SlashSquare,
     Sliders,
     SlidersAlt,
     Snip,
@@ -320,6 +323,7 @@ impl IconName {
             IconName::Disconnected => "icons/disconnected.svg",
             IconName::Download => "icons/download.svg",
             IconName::Ellipsis => "icons/ellipsis.svg",
+            IconName::EllipsisVertical => "icons/ellipsis_vertical.svg",
             IconName::Envelope => "icons/feedback.svg",
             IconName::Escape => "icons/escape.svg",
             IconName::ExclamationTriangle => "icons/warning.svg",
@@ -396,6 +400,8 @@ impl IconName {
             IconName::Server => "icons/server.svg",
             IconName::Settings => "icons/file_icons/settings.svg",
             IconName::Shift => "icons/shift.svg",
+            IconName::Slash => "icons/slash.svg",
+            IconName::SlashSquare => "icons/slash_square.svg",
             IconName::Sliders => "icons/sliders.svg",
             IconName::SlidersAlt => "icons/sliders-alt.svg",
             IconName::Snip => "icons/snip.svg",