refactor: Improve keymap upgrader

Moved the keymap upgrader to a top-level page like the power profiler
to make it more discoverable. It upgrades more things than key codes
now, so putting it in the codes category doesn't make much sense.

Converted the upgrader code to TypeScript and split it up into smaller
files to make it easier to add new upgrade functions.

Added upgrade functions to remove/replace "label" properties and rename
matrix-transform.h to matrix_transform.h.

docs/docusaurus.config.js

@@ -55,6 +55,11 @@ module.exports = {
           label: "Power Profiler",
           position: "left",
         },
+        {
+          to: "keymap-upgrader",
+          label: "Keymap Upgrader",
+          position: "left",
+        },
         {
           href: "https://github.com/zmkfirmware/zmk",
           label: "GitHub",