fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/components/common/show-if/show-if.tsx

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { PropsWithChildren } from 'react'
+import React, { Fragment } from 'react'
+
+export interface ShowIfProps {
+  condition: boolean
+}
+
+/**
+ * Renders the children if the condition is met.
+ *
+ * @param children The children to show if the condition is met.
+ * @param condition If the children should be shown
+ */
+export const ShowIf: React.FC<PropsWithChildren<ShowIfProps>> = ({ children, condition }) => {
+  return condition ? <Fragment>{children}</Fragment> : null
+}