Update to latest rumdl release and enable another option (#7483)

The `style = "fixed"` is partially implied by `indent = 4`, but not
fully in some specific cases. There were also bugs in fully applying it
that are now fixed, and so we can specify it explicitly to get rumdl to
canonicalize nested list indentation more thoroughly.

Assisted-by: Antigravity with Gemini

utils/vscode/development.md

@@ -37,8 +37,8 @@ This installs `vsce` and `ovsx` to `/usr/local/bin`. Ensure that
     -   Using the UI:
 
         1.  `npm install && vsce package -o carbon.vsix && realpath carbon.vsix`
-             -   This installs dependencies, builds the VSIX file, and prints the
-                 path.
+            -   This installs dependencies, builds the VSIX file, and prints the
+                path.
         2.  Open the
             [command palette](https://code.visualstudio.com/docs/getstarted/userinterface#_command-palette)
             and select "Extensions: Install from VSIX...".
@@ -51,9 +51,9 @@ This installs `vsce` and `ovsx` to `/usr/local/bin`. Ensure that
          1.  `npm install && vsce package -o carbon.vsix && realpath carbon.vsix`
          2.  Go to
              https://marketplace.visualstudio.com/manage/publishers/carbon-lang
-              -   We use `infra-role@carbon-lang.dev` for publishing; the GitHub
-                  account `CarbonInfraBot` can also be used for login. Contact leads
-                  if you require access.
+             -   We use `infra-role@carbon-lang.dev` for publishing; the GitHub
+                 account `CarbonInfraBot` can also be used for login. Contact leads
+                 if you require access.
          3.  Next to the extension name, click the "..." and select "Update".
          4.  Select the `carbon.vsix` file.
     3.  Build and publish to the Open VSX Registry by following the