Add KC_DICTATION keycode for macOS Dictation

[ankitsxchdeva]

Description

Adds KC_DICTATION mapping to the standard usage 0x0CF. Requires EXTRAKEY_ENABLE

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

This could be handled just as well as a community module.

Eg:
https://github.com/drashna/qmk_modules/blob/main/extra_extra_key/extra_extra_key.c

[ankitsxchdeva]

I looked at the module route but selfishly wanted this change in core so that downstream forks like via/vial could add it.

It's a standard HID code, not custom behavior. It's also appended at the end of the consumer range so there are no shifts required.

Also it's consistent with the other core keycodes:

KC_ASSISTANT       = 0x00C0
KC_MISSION_CONTROL = 0x00C1
KC_LAUNCHPAD       = 0x00C2

I can close it out if you disagree!

[R1DEN]

@ankitsxchdeva agree on this one, this is a standard mac button. so it does make sense to have it as a core part, if it IS is in fact a stock button on a major patform (MacOS) and not just an edge case on some custom device.