[Core] Add Caps Word feature to core (#16588)

Co-authored-by: precondition <57645186+precondition@users.noreply.github.com>
Co-authored-by: Drashna Jaelre <drashna@live.com>

quantum/caps_word.h

@@ -0,0 +1,43 @@
+// Copyright 2021-2022 Google LLC
+//
+// 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
+//
+//     https://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.
+
+#pragma once
+
+#include "quantum.h"
+
+#ifndef CAPS_WORD_IDLE_TIMEOUT
+#    define CAPS_WORD_IDLE_TIMEOUT 5000 // Default timeout of 5 seconds.
+#endif                                  // CAPS_WORD_IDLE_TIMEOUT
+
+#if CAPS_WORD_IDLE_TIMEOUT > 0
+/** @brief Matrix scan task for Caps Word feature */
+void caps_word_task(void);
+
+/** @brief Resets timer for Caps Word idle timeout. */
+void caps_word_reset_idle_timer(void);
+#else
+static inline void caps_word_task(void) {}
+#endif // CAPS_WORD_IDLE_TIMEOUT > 0
+
+void caps_word_on(void);     /**< Activates Caps Word. */
+void caps_word_off(void);    /**< Deactivates Caps Word. */
+void caps_word_toggle(void); /**< Toggles Caps Word. */
+bool is_caps_word_on(void);  /**< Gets whether currently active. */
+
+/**
+ * @brief Caps Word set callback.
+ *
+ * @param active True if Caps Word is active, false otherwise
+ */
+void caps_word_set_user(bool active);