Improve VoiceOver & WebKit accessibility support

Based on https://bugs.webkit.org/show_bug.cgi?id=167671#c15
(workaround)

src/autocomplete/AutocompleteProvider.tsx

@@ -27,11 +27,11 @@ export interface ICommand {
     };
 }
 
-export default class AutocompleteProvider {
+export default abstract class AutocompleteProvider {
     commandRegex: RegExp;
     forcedCommandRegex: RegExp;
 
-    constructor(commandRegex?: RegExp, forcedCommandRegex?: RegExp) {
+    protected constructor(commandRegex?: RegExp, forcedCommandRegex?: RegExp) {
         if (commandRegex) {
             if (!commandRegex.global) {
                 throw new Error('commandRegex must have global flag set');
@@ -93,18 +93,11 @@ export default class AutocompleteProvider {
         };
     }
 
-    async getCompletions(query: string, selection: ISelectionRange, force = false): Promise<ICompletion[]> {
-        return [];
-    }
+    abstract getCompletions(query: string, selection: ISelectionRange, force: boolean): Promise<ICompletion[]>;
 
-    getName(): string {
-        return 'Default Provider';
-    }
+    abstract getName(): string;
 
-    renderCompletions(completions: React.ReactNode[]): React.ReactNode | null {
-        console.error('stub; should be implemented in subclasses');
-        return null;
-    }
+    abstract renderCompletions(completions: React.ReactNode[]): React.ReactNode | null;
 
     // Whether we should provide completions even if triggered forcefully, without a sigil.
     shouldForceComplete(): boolean {

src/autocomplete/CommandProvider.tsx

@@ -91,7 +91,7 @@ export default class CommandProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_block"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Command Autocomplete")}
             >
                 { completions }

src/autocomplete/CommunityProvider.tsx

@@ -112,7 +112,7 @@ export default class CommunityProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill mx_Autocomplete_Completion_container_truncate"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Community Autocomplete")}
             >
                 { completions }

src/autocomplete/DuckDuckGoProvider.tsx

@@ -99,7 +99,7 @@ export default class DuckDuckGoProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_block"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("DuckDuckGo Results")}
             >
                 { completions }

src/autocomplete/EmojiProvider.tsx

@@ -140,7 +140,7 @@ export default class EmojiProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Emoji Autocomplete")}
             >
                 { completions }

src/autocomplete/NotifProvider.tsx

@@ -66,7 +66,7 @@ export default class NotifProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill mx_Autocomplete_Completion_container_truncate"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Notification Autocomplete")}
             >
                 { completions }

src/autocomplete/RoomProvider.tsx

@@ -123,7 +123,7 @@ export default class RoomProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill mx_Autocomplete_Completion_container_truncate"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("Room Autocomplete")}
             >
                 { completions }

src/autocomplete/UserProvider.tsx

@@ -178,7 +178,7 @@ export default class UserProvider extends AutocompleteProvider {
         return (
             <div
                 className="mx_Autocomplete_Completion_container_pill"
-                role="listbox"
+                role="presentation"
                 aria-label={_t("User Autocomplete")}
             >
                 { completions }