chore(Communities/InDropdown): performance improved

- removed multiple filtering separately for each category
- no instantiation of all delegates up front (regular ListView approach
  used)
- fixed category selection when filtering - selecting/deselecting only
  items fulfilling search criteria
- significant simplification of the code

Closes: #14275

storybook/pages/InDropdownPage.qml

@@ -1,6 +1,6 @@
-import QtQuick 2.14
-import QtQuick.Controls 2.14
-import QtQuick.Layouts 1.14
+import QtQuick 2.15
+import QtQuick.Controls 2.15
+import QtQuick.Layouts 1.15
 
 import AppLayouts.Communities.popups 1.0
 

storybook/src/Models/ChannelsModel.qml

@@ -81,6 +81,86 @@ ListModel {
         icon: ""
         colorId: 4
     }
+    ListElement {
+        itemId: "_report-scam2"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam2"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam3"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam3"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam4"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam4"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam5"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam5"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam6"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam6"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam7"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam7"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam8"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam8"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
+    ListElement {
+        itemId: "_report-scam9"
+        isCategory: false
+        categoryId: "_support"
+        name: "report-scam9"
+        emoji: ""
+        color: ""
+        icon: ""
+        colorId: 4
+    }
     ListElement {
         itemId: ""
         isCategory: true