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/hooks/common/use-boolean-state.ts

@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { useCallback, useState } from 'react'
+
+/**
+ * Provides a boolean state and two functions that set the boolean to true or false.
+ *
+ * @param initialState The initial value of the state
+ * @return An array containing the state, and two functions that set the state value to true or false.
+ */
+export const useBooleanState = (
+  initialState: boolean | (() => boolean) = false
+): [state: boolean, setToTrue: () => void, setToFalse: () => void] => {
+  const [state, setState] = useState(initialState)
+  const setToFalse = useCallback(() => setState(false), [])
+  const setToTrue = useCallback(() => setState(true), [])
+
+  return [state, setToTrue, setToFalse]
+}