Improve VS Code Python settings (#2860)

chore: Fix deprecated vscode Python formatter

The python.formatting.provider setting was deprecated in favor of
having a separate extension for each Python formatter and using
editor.defaultFormatter instead. This adds a recommendation for the
Black formatter extension and selects it for Python files.

chore: Limit vscode Python analysis paths

This limits vscode's Python analysis to the scripts folders so it
doesn't slow down trying to scan all of Zephyr.

.vscode/extensions.json

@@ -1,6 +1,7 @@
 {
   "recommendations": [
     "esbenp.prettier-vscode",
+    "ms-python.black-formatter",
     "ms-python.python",
     "ms-vscode.cpptools",
     "plorefice.devicetree",

.vscode/settings.json

@@ -3,7 +3,7 @@
     "*.overlay": "dts",
     "*.keymap": "dts"
   },
-  "python.formatting.provider": "black",
+  "python.analysis.include": ["app/scripts", "zephyr/scripts"],
   "[c]": {
     "editor.formatOnSave": true
   },
@@ -13,7 +13,7 @@
   },
   "[python]": {
     "editor.formatOnSave": true,
-    "editor.defaultFormatter": "ms-python.python"
+    "editor.defaultFormatter": "ms-python.black-formatter"
   },
   "[css][json][jsonc][html][markdown][yaml]": {
     "editor.formatOnSave": true,