feat: Add keyboard physical layout system.

* Add bindings to allow creating multiple physical layouts that specify
  their key's physical attributes, and the matching matrix transform
  and dependant kscan to use.
* Synthesize a basic physical layout if none specified, for backwards
  compatibility.
* Update matrix transform API to explicitly pass in the selected transform
  to the API instead of using a fixed chosen transform.
* Move kscan subscription and handling into the physical layout code, so
  that selecting a different physical layout at runtime can also use the
  correct kscan instance.
* Add `physical_layouts.dtsi` file to include so you can use the
  pre-configured `&key_physical_attrs` for adding you layout keys.

app/dts/bindings/zmk,key-physical-attrs.yaml

@@ -0,0 +1,24 @@
+#
+# Copyright (c) 2024 The ZMK Contributors
+#
+# SPDX-License-Identifier: MIT
+
+description: |
+  The physical attributes of a key, including size, location, and rotation
+
+compatible: "zmk,key-physical-attrs"
+
+properties:
+  "#key-cells":
+    type: int
+    required: true
+    const: 7
+
+key-cells:
+  - width
+  - height
+  - x
+  - y
+  - r
+  - rx
+  - ry