LED Matrix: add led_matrix_types.h and implement g_led_config

[fauxpark]

Description

First part of LED Matrix revival. Since there are no animations defined, I can only test that it compiles successfully.

Some notes:

I had to rename the EEPROM config struct led_config_t (RGB Matrix equivalent rgb_config_t) to led_eeconfig_t as otherwise it would conflict with the led_config_t of g_led_configs. IMO this should be done for RGB Matrix as well, though there is no conflict there.

clueboard/66_hotswap/gen1 is currently the only consumer of LED Matrix (terrazzo also uses it but seems to have its own animation system). @skullydazed would you mind checking if the g_led_config I've created matches the board?

I copied over the (currently unused) flags defines, but omitted the underglow one - wondering if this could still be useful for boards with single-colour underglow (I don't know of any, though).

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).