Add symbol filter to outline pane

data/Application.css

@@ -69,3 +69,11 @@ textview.scrubber {
 .fuzzy-item.preselect-fuzzy label {
     opacity: 0.7;
 }
+
+.symbol-outline > box.horizontal {
+    margin: 1em;
+}
+
+.symbol-outline .sidebar {
+    background: inherit;
+}

data/io.elementary.code.gresource.xml

@@ -29,4 +29,7 @@
     <file alias="scalable/actions/panel-right-rtl-symbolic.svg" compressed="true" preprocess="xml-stripblanks">icons/panel-right-rtl-symbolic.svg</file>
     <file alias="scalable/actions/panel-right-symbolic.svg" compressed="true" preprocess="xml-stripblanks">icons/panel-right-symbolic.svg</file>
   </gresource>
+  <gresource prefix="/io/elementary/code/icons">
+    <file alias="scalable/actions/filter-symbolic.svg" compressed="true" preprocess="xml-stripblanks">icons/filter-symbolic.svg</file>
+  </gresource>
 </gresources>

src/SymbolPane/C/CtagsSymbol.vala

@@ -18,10 +18,25 @@
 
 public class Scratch.Services.CtagsSymbol : Code.Widgets.SourceList.ExpandableItem {
     public Scratch.Services.Document doc { get; construct set; }
+    public SymbolType symbol_type { get; set; default = SymbolType.OTHER; }
     public int line { get; construct set; }
 
-    public CtagsSymbol (Scratch.Services.Document doc, string name, int line, Icon? _icon) {
-        Object (doc: doc, name: name, line: line);
+    public CtagsSymbol (
+        Scratch.Services.Document doc,
+        string name,
+        int line,
+        Icon? _icon,
+        SymbolType? s_type = null) {
+
+        Object (
+            doc: doc,
+            name: name,
+            line: line
+        );
+
         icon = _icon;
+        if (s_type != null) {
+            symbol_type = s_type;
+        }
     }
 }

src/SymbolPane/C/CtagsSymbolIter.vala

@@ -21,8 +21,22 @@ public class Scratch.Services.CtagsSymbolIter : Object {
     public string parent { get; construct set; }
     public int line { get; construct set; }
     public Icon? icon { get; construct set; }
+    public SymbolType? symbol_type;
 
-    public CtagsSymbolIter (string name, string parent, int line, Icon? icon) {
-        Object (name: name, parent: parent, line: line, icon: icon);
+    public CtagsSymbolIter (
+        string name,
+        string parent,
+        int line,
+        Icon? icon,
+        SymbolType? s_type = SymbolType.OTHER) {
+
+        Object (
+            name: name,
+            parent: parent,
+            line: line,
+            icon: icon
+        );
+
+        symbol_type = s_type;
     }
 }