settings: Add an experimental flag to toggle rendering KaTeX

Following commits will add ability to render some basic KaTeX content,
where rendering of some KaTeX content would be broken. So, add an
experimental flag which is disabled by default, and allows the user
or developer to explicitly enable and test the rendering of KaTeX content.

Author: rajveermalviya

lib/model/settings.dart

@@ -110,6 +110,9 @@ enum BoolGlobalSetting {
   /// (Having one stable value in this enum is also handy for tests.)
   placeholderIgnore(GlobalSettingType.placeholder, false),
 
+  /// An experimental flag to toggle rendering KaTeX content in messages.
+  renderKatex(GlobalSettingType.experimentalFeatureFlag, false),
+
   // Former settings which might exist in the database,
   // whose names should therefore not be reused:
   // (this list is empty so far)

test/model/settings_test.dart

@@ -79,42 +79,63 @@ void main() {
       final globalSettings = eg.globalStore(boolGlobalSettings: {}).settings;
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isFalse();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isFalse();
       assert(!BoolGlobalSetting.placeholderIgnore.default_);
+      assert(!BoolGlobalSetting.renderKatex.default_);
     });
 
     test('get from initial load', () {
       final globalSettings = eg.globalStore(boolGlobalSettings: {
         BoolGlobalSetting.placeholderIgnore: true,
+        BoolGlobalSetting.renderKatex: true,
       }).settings;
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isTrue();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isTrue();
     });
 
     test('set, get', () async {
       final globalSettings = eg.globalStore(boolGlobalSettings: {}).settings;
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isFalse();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isFalse();
 
       await globalSettings.setBool(BoolGlobalSetting.placeholderIgnore, true);
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, true);
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isTrue();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isTrue();
 
       await globalSettings.setBool(BoolGlobalSetting.placeholderIgnore, false);
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, false);
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isFalse();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isFalse();
     });
 
     test('set to null -> revert to default', () async {
       final globalSettings = eg.globalStore(boolGlobalSettings: {
         BoolGlobalSetting.placeholderIgnore: true,
+        BoolGlobalSetting.renderKatex: true,
       }).settings;
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isTrue();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isTrue();
 
       await globalSettings.setBool(BoolGlobalSetting.placeholderIgnore, null);
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, null);
       check(globalSettings).getBool(BoolGlobalSetting.placeholderIgnore)
         .isFalse();
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex)
+        .isFalse();
       assert(!BoolGlobalSetting.placeholderIgnore.default_);
+      assert(!BoolGlobalSetting.renderKatex.default_);
     });
   });
 }