Add dialpad to transfer dialog + various dialpad UI improvements (#6363)

Co-authored-by: Germain <germain@souquet.com>
Co-authored-by: Andrew Morgan <andrew@amorgan.xyz>
Co-authored-by: David Baker <dbkr@users.noreply.github.com>

src/components/views/elements/DialPadBackspaceButton.tsx

@@ -0,0 +1,31 @@
+/*
+Copyright 2021 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 "./AccessibleButton";
+
+interface IProps {
+    // Callback for when the button is pressed
+    onBackspacePress: () => void;
+}
+
+export default class DialPadBackspaceButton extends React.PureComponent<IProps> {
+    render() {
+        return <div className="mx_DialPadBackspaceButtonWrapper">
+            <AccessibleButton className="mx_DialPadBackspaceButton" onClick={this.props.onBackspacePress} />
+        </div>;
+    }
+}