Implement XAP style merge semantics for DD keycodes

[zvecr]

Description

keycodes_0.0.2_quantum.hjson could contain the following to ignore any existing keycodes

{
    "keycodes": {
        "!reset!":0,

        "0x7C00": {
            "group": "quantum",
            "key": "QK_BOOTLOADER",
            "aliases": [
                "QK_BOOT"
            ]
        },
    }
}

Likewise keycodes_0.0.2.hjson could contain the following to ignore any existing ranges

{
    "ranges": {
        "!reset!":0,

        "0x0000/0x00FF": {
            "define": "QK_BASIC"
        },
    }
}

Types of Changes

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