Revise and clean up some icons (#35582)

This is really just a small beginning, as there are many other icons to
be revised and cleaned up. Our current set is a bit of a mess in terms
of dimension, spacing, stroke width, and terminology. I'm sure there are
more non-used icons I'm not covering here, too. We'll hopefully tackle
it all soon leading up to 1.0.

Closes https://github.com/zed-industries/zed/issues/35576

Release Notes:

- N/A

crates/icons/src/icons.rs

@@ -38,7 +38,6 @@ pub enum IconName {
     ArrowUpFromLine,
     ArrowUpRight,
     ArrowUpRightAlt,
-    AtSign,
     AudioOff,
     AudioOn,
     Backspace,
@@ -48,15 +47,13 @@ pub enum IconName {
     BellRing,
     Binary,
     Blocks,
-    Bolt,
+    BoltOutlined,
     BoltFilled,
-    BoltFilledAlt,
     Book,
     BookCopy,
-    BookPlus,
-    Brain,
     BugOff,
     CaseSensitive,
+    Chat,
     Check,
     CheckDouble,
     ChevronDown,
@@ -184,14 +181,9 @@ pub enum IconName {
     Maximize,
     Menu,
     MenuAlt,
-    MessageBubbles,
     Mic,
     MicMute,
-    Microscope,
     Minimize,
-    NewFromSummary,
-    NewTextThread,
-    NewThread,
     Option,
     PageDown,
     PageUp,
@@ -202,9 +194,7 @@ pub enum IconName {
     PersonCircle,
     PhoneIncoming,
     Pin,
-    Play,
-    PlayAlt,
-    PlayBug,
+    PlayOutlined,
     PlayFilled,
     Plus,
     PocketKnife,
@@ -221,7 +211,6 @@ pub enum IconName {
     ReplyArrowRight,
     Rerun,
     Return,
-    Reveal,
     RotateCcw,
     RotateCw,
     Route,
@@ -246,7 +235,6 @@ pub enum IconName {
     Sparkle,
     SparkleAlt,
     SparkleFilled,
-    Spinner,
     Split,
     SplitAlt,
     SquareDot,
@@ -256,7 +244,6 @@ pub enum IconName {
     StarFilled,
     Stop,
     StopFilled,
-    Strikethrough,
     Supermaven,
     SupermavenDisabled,
     SupermavenError,
@@ -266,6 +253,9 @@ pub enum IconName {
     Terminal,
     TerminalAlt,
     TextSnippet,
+    TextThread,
+    Thread,
+    ThreadFromSummary,
     ThumbsDown,
     ThumbsUp,
     TodoComplete,
@@ -285,7 +275,6 @@ pub enum IconName {
     ToolTerminal,
     ToolWeb,
     Trash,
-    TrashAlt,
     Triangle,
     TriangleRight,
     Undo,