feat(select): support vuetify2-style select headers

Support 'header' entries in sw-select items list to maintain support from
vuetify2 syntax

Author: Jo-Byr

examples/01_Widgets/definitions/model.yaml

@@ -205,6 +205,29 @@ Select:
           - text: Case 4
             value: 4
 
+  Section:
+    _label: Drop Down with sub-sections
+    _help: >-
+      Example of a drop down with sub-sections
+    type: string
+    size: -1
+    initial:
+      - A
+      - '1'
+    domains:
+      - type: LabelList
+        values:
+          - header: Letter cases
+          - text: Case A
+            value: A
+          - text: Case B
+            value: B
+          - header: Number cases
+          - text: Case 1
+            value: '1'
+          - text: Case 2
+            value: '2'
+
   SelectDynamicList:
     _label: Dynamic available
     _help: Just to try remote domain list

vue3-components/src/widgets/Select/template.html

@@ -13,5 +13,13 @@
     :persistent-hint="!!(useRangeHelp || help)"
     :disabled="disabled || !decorator.enable"
     :readonly="readonly"
-  />
-</v-col>
+  >
+    <template #item="{ item, props }">
+      <v-list-subheader v-if="item.raw.header">
+        {{ item.raw.header }}
+      </v-list-subheader>
+
+      <v-list-item v-else v-bind="props" />
+    </template>
+  </v-select>
+ </v-col>