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,physical-layout-position-map.yaml

@@ -0,0 +1,23 @@
+#
+# Copyright (c) 2024 The ZMK Contributors
+#
+# SPDX-License-Identifier: MIT
+
+description: |
+  Describes how to correlate equivalent keys between layouts that don't have the exact same X,Y location.
+
+compatible: "zmk,physical-layout-position-map"
+
+properties:
+  complete:
+    type: boolean
+    description: If the mapping complete describes the key mapping, and no position based mapping should be used.
+
+child-binding:
+  properties:
+    physical-layout:
+      type: phandle
+      description: The physical layout that corresponds to this mapping entry.
+    positions:
+      type: array
+      description: Array of key positions that match the same array entry in the other sibling nodes.