Generate and use constants for pocketmine.yml constant names

a couple of usages of properties that no longer exist couldn't be migrated.
in addition, this revealed a couple of dead properties in the default file.

this is not an ideal solution (I'd much rather model the configs using classes and map them) but in the absence of a good and reliable library to do that, this is the next best thing.

.github/workflows/main.yml

@@ -158,6 +158,9 @@ jobs:
       - name: Regenerate BedrockData available files constants
         run: php build/generate-bedrockdata-path-consts.php
 
+      - name: Regenerate YmlServerProperties constants
+        run: php build/generate-pocketmine-yml-property-consts.php
+
       - name: Verify code is unchanged
         run: |
           git diff