Convert zinc to use split_common

[zvecr]

Description

Left some config in which ideally should be removed, like changing the default tapping term. But the target is to maintain backwards compatibility with existing keymaps.

Tagging @monksoffunk as maintainer.

TODO:

• Swap to RGBLED_SPLIT and confirm led behaviour

Types of Changes

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

Checklist

• My code follows the code style of this project.
• 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).

[monksoffunk]

Thanks for your contributions!
I've already prepared the split_common version.
https://github.com/monksoffunk/qmk_firmware/tree/zinc_splitcommon/keyboards/zinc

Also, I've done the RGB Matrix version based on the current zinc codes, cause the RGB Matrix is not fully compatible with split_common.
https://github.com/monksoffunk/qmk_firmware/tree/zinc_RGB_matrix/keyboards/zinc

So I can't decide which version should I PR...

[drashna]

@monksoffunk Split common needs something like #5998 to work properly with some of the rgb matrix effects.

[zvecr]

A RGBLED_SPLIT version can be deployed right now, where a fully working RGB matrix version that isnt using the crkbd method of building 2 different firmwares will be blocked on the PR Drashna mentions.

Given some recent hardware issues, my preference would be to migrate to split_common where possible.

And as a final side note, your "split_common" version would have to go through the breaking changes process, as it changes user keymaps.

[monksoffunk]

@zvecr @drashna
Thanks to you, I opened #7114.