Add support for disabling spell checking (#8604)

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/elements/Dropdown.tsx

@@ -82,6 +82,8 @@ interface IProps {
     // width.
     menuWidth?: number;
     searchEnabled?: boolean;
+    // Placeholder to show when no value is selected
+    placeholder?: string;
     // Called when the selected option changes
     onOptionChange(dropdownKey: string): void;
     // Called when the value of the search field changes
@@ -362,7 +364,7 @@ export default class Dropdown extends React.Component<IProps, IState> {
                 this.props.getShortOption(this.props.value) :
                 this.childrenByKey[this.props.value];
             currentValue = <div className="mx_Dropdown_option" id={`${this.props.id}_value`}>
-                { selectedChild }
+                { selectedChild || this.props.placeholder }
             </div>;
         }
 

src/components/views/elements/SpellCheckLanguagesDropdown.tsx

@@ -116,7 +116,9 @@ export default class SpellCheckLanguagesDropdown extends React.Component<SpellCh
             onSearchChange={this.onSearchChange}
             searchEnabled={true}
             value={value}
-            label={_t("Language Dropdown")}>
+            label={_t("Language Dropdown")}
+            placeholder={_t("Choose a locale")}
+        >
             { options }
         </Dropdown>;
     }

src/components/views/elements/ToggleSwitch.tsx

@@ -25,7 +25,7 @@ interface IProps {
     checked: boolean;
 
     // Whether or not the user can interact with the switch
-    disabled: boolean;
+    disabled?: boolean;
 
     // Called when the checked state changes. First argument will be the new state.
     onChange(checked: boolean): void;