Runes Skjöldr Touch-Up (#17792)

* skjoldr.h: use ___ for KC_NO

* skjoldr.h: use K<row><column> notation

Matrix was previously defined using identifiers in the format of K<column><row>.

* skjoldr.h: add matrix diagram

* info.json: apply friendly formatting

- key legends as labels
- correct key sizes and positioning

* refactor keymaps

Refactors the `default` and `via` keymaps.

- use QMK-native keycode aliases
- grid-align keycodes for readability

* rename LAYOUT macro to LAYOUT_60_ansi_arrow

* enable Community Layout support

* info.json: correct maintainer value

Field is meant to reference the maintainer's GitHub username.

keyboards/runes/skjoldr/rules.mk

@@ -16,3 +16,5 @@ NKRO_ENABLE = yes           # Enable N-Key Rollover
 BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
 RGBLIGHT_ENABLE = no        # Enable keyboard RGB underglow
 AUDIO_ENABLE = no           # Audio output
+
+LAYOUTS = 60_ansi_arrow