implement ChoiceSetting for settings modal similar to BooleanSetting

src/components/settings_modal/tabs/general_tab.js

@@ -1,5 +1,5 @@
 import BooleanSetting from '../helpers/boolean_setting.vue'
-import Select from '../../select/select.vue'
+import ChoiceSetting from '../helpers/choice_setting.vue'
 import InterfaceLanguageSwitcher from 'src/components/interface_language_switcher/interface_language_switcher.vue'
 
 import SharedComputedObject from '../helpers/shared_computed_object.js'
@@ -15,6 +15,11 @@ library.add(
 const GeneralTab = {
   data () {
     return {
+      subjectLineOptions: ['email', 'noop', 'masto'].map(mode => ({
+        key: mode,
+        value: mode,
+        label: this.$t(`settings.subject_line_${mode === 'masto' ? 'mastodon' : mode}`)
+      })),
       loopSilentAvailable:
       // Firefox
       Object.getOwnPropertyDescriptor(HTMLVideoElement.prototype, 'mozHasAudio') ||
@@ -26,13 +31,20 @@ const GeneralTab = {
   },
   components: {
     BooleanSetting,
-    InterfaceLanguageSwitcher,
-    Select
+    ChoiceSetting,
+    InterfaceLanguageSwitcher
   },
   computed: {
     postFormats () {
       return this.$store.state.instance.postFormats || []
     },
+    postContentOptions () {
+      return this.postFormats.map(format => ({
+        key: format,
+        value: format,
+        label: this.$t(`post_status.content_type["${format}"]`)
+      }))
+    },
     instanceSpecificPanelPresent () { return this.$store.state.instance.showInstanceSpecificPanel },
     instanceWallpaperUsed () {
       return this.$store.state.instance.background &&