Add a dialpad UI for PSTN lookup

Queries the homeserver for PSTN protocol support, and if found,
the add-room button on the DM rooms list section opens a context
menu instead with a 'dial pad' option as well as the current 'start chat'
dialog. Entering a number into this and pressing dial performs
a thirdparty user query for the given string and starts a DM with that
user.

src/components/views/voip/DialPad.tsx

@@ -0,0 +1,82 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import * as React from "react";
+import AccessibleButton from "../elements/AccessibleButton";
+
+const BUTTONS = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '*', '0', '#'];
+
+enum DialPadButtonKind {
+    Digit,
+    Delete,
+    Dial,
+}
+
+interface IButtonProps {
+    kind: DialPadButtonKind;
+    digit?: string;
+    onButtonPress: (string) => void;
+}
+
+class DialPadButton extends React.PureComponent<IButtonProps> {
+    onClick = () => {
+        this.props.onButtonPress(this.props.digit);
+    }
+
+    render() {
+        switch (this.props.kind) {
+            case DialPadButtonKind.Digit:
+                return <AccessibleButton className="mx_DialPad_button" onClick={this.onClick}>
+                    {this.props.digit}
+                </AccessibleButton>;
+            case DialPadButtonKind.Delete:
+                return <AccessibleButton className="mx_DialPad_button mx_DialPad_deleteButton"
+                    onClick={this.onClick}
+                />;
+            case DialPadButtonKind.Dial:
+                return <AccessibleButton className="mx_DialPad_button mx_DialPad_dialButton" onClick={this.onClick} />;
+        }
+    }
+}
+
+interface IProps {
+    onDigitPress: (string) => void;
+    onDeletePress: (string) => void;
+    onDialPress: (string) => void;
+}
+
+export default class Dialpad extends React.PureComponent<IProps> {
+    render() {
+        const buttonNodes = [];
+
+        for (const button of BUTTONS) {
+            buttonNodes.push(<DialPadButton key={button} kind={DialPadButtonKind.Digit}
+                digit={button} onButtonPress={this.props.onDigitPress}
+            />);
+        }
+
+        buttonNodes.push(<DialPadButton key="del" kind={DialPadButtonKind.Delete}
+            onButtonPress={this.props.onDeletePress}
+        />);
+        buttonNodes.push(<DialPadButton key="dial" kind={DialPadButtonKind.Dial}
+            onButtonPress={this.props.onDialPress}
+        />);
+
+        return <div className="mx_DialPad">
+            {buttonNodes}
+        </div>;
+    }
+}