[XAP] implement keyboard- and user-level xap.json

[tzarc]

XAP Task Info

Original Issue
Original spec document
Current XAP Definitions
Current XAP Generated Docs
Placeholder PR

Description

Any work in this area needs to be discussed with QMK Collaborators first.

Add support for keyboard-level and user-level xap.json to be provided, such that it's merged and included in the firmware.

[stale]

This issue has been automatically marked as stale because it has not had activity in the last 90 days. It will be closed in the next 30 days unless it is tagged properly or other activity occurs.
For maintainers: Please label with bug, in progress, on hold, discussion or to do to prevent the issue from being re-flagged.

[zvecr]

Currently implemented with the following:

• xap.hjson to match up with xap_<version>.hjson
• user/keyboard specs can only augment the 2 "special" routes
  • this limitation protects core functionality from overrides
• Validation does not currently handle the invalid case of type: command with routes: { ... }
  • jsonschema doesnt seem to provide the ability to validate an object based on a child keys value
• docs/codegen will ignore user/keyboard level customisation
• user/keyboard broadcast_messages?