Disable format on save for C and C++ (#10141)

We want Zed to be opinionated and low-configuration. Your code editor
should get out of the way, and just do the right thing.

However, some ecosystems aren't opinionated enough for us to
automatically detect the right way to format your code, so let's turn it
off.

Release Notes:

- Disabled `format_on_save` by default in C and C++.

assets/settings/default.json

@@ -545,6 +545,12 @@
   "file_types": {},
   // Different settings for specific languages.
   "languages": {
+    "C++": {
+      "format_on_save": "off"
+    },
+    "C": {
+      "format_on_save": "off"
+    },
     "Plain Text": {
       "soft_wrap": "preferred_line_length"
     },