KBDfans KBD66 Layout Additions and Refactor (#20693)

* add matrix_diagram.md

* info.json: apply friendly formatting

* add LAYOUT_66_ansi_split_space

* add LAYOUT_66_iso_split_space

* refactor default keymap

- use four-space indent
- use QMK-native keycode aliases directly
- use `enum` statement for layer names
- grid-align keycodes

* refactor ansi keymap

- use four-space indent
- use QMK-native keycode aliases directly
- use `enum` statement for layer names
- grid-align keycodes

* refactor iso keymap

- use four-space indent
- use QMK-native keycode aliases directly
- use `enum` statement for layer names
- grid-align keycodes

* change layout macro for ansi keymap

Refactors the `ansi` keymap to use the `LAYOUT_66_ansi_split_space` macro, and renames the keymap to `default_ansi_split_space`.

* change layout macro for iso keymap

Refactors the `iso` keymap to use the `LAYOUT_66_iso_split_space` macro, and renames the keymap to `default_iso_split_space`.

* add LAYOUT_66_ansi

The column for the spacebar key may be wrong; I was unable to find high-resolution images of the PCB.

* add LAYOUT_66_iso

The column for the spacebar key may be wrong; I was unable to find high-resolution images of the PCB.

* enable Community Layout support

keyboards/kbdfans/kbd66/keymaps/default_iso_split_space/readme.md

@@ -0,0 +1,11 @@
+# ISO keymap for KBD66
+
+![KBD66 Layout Image](https://i.imgur.com/q6GTOsb.jpg)
+
+Standard ISO layout for KBD66.  
+Cycle backlight: Fn + .  
+Backlight breathing: Fn + ,  
+Volume Up/Down: Fn + [ and Fn + ]  
+Mute: Fn + #  
+Sleep: Fn + /  
+Bootloader Mode: Fn + CapsLock