[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/process_keycode/process_caps_word.h

@@ -0,0 +1,37 @@
+// 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"
+#include "caps_word.h"
+
+/**
+ * @brief Process handler for Caps Word feature.
+ *
+ * @param keycode  Keycode registered by matrix press, per keymap
+ * @param record   keyrecord_t structure
+ * @return true    Continue processing keycodes, and send to host
+ * @return false   Stop processing keycodes, and don't send to host
+ */
+bool process_caps_word(uint16_t keycode, keyrecord_t* record);
+
+/**
+ * @brief Weak function for user-level Caps Word press modification.
+ *
+ * @param keycode   Keycode registered by matrix press, per keymap
+ * @return true     Continue Caps Word
+ * @return false    Stop Caps Word
+ */
+bool caps_word_press_user(uint16_t keycode);