lint: Transition to gjs' object spacing rule

When gjs overhauled its coding style, it opted for disallowing
spaces around braces in object literals: `{foo: 42}`.

We opted out of that particular rule in commit 09b8e8f, primarily
because it would have been a very intrusive change with the old
style of object literals:

```js
   let oldStyle = { foo: 42,
                    bar: 23 };
```

Alas, all multi-line object literals have been transitioned to
the new style where braces go on separate lines, so they are no
longer subject to the rule one way or the other.

Nowadays the rule mostly affects destructuring, and there it
is a bit odd to apply different spacing rules to arrays and
objects:

```js
    const [foo, bar] = someArray;
    const { baz, quz } = someObject;
```

This is now the main divergence from the canonical gnome style,
and the only one where we directly contradict it.

It would be good to transition away from that, and as the rule
now only affect destructuring and single-line object literals,
we can do that on a case-by-case bases by moving the override
to the legacy configuration.

As desctructuring imports makes up a fair share of the affected
code, and those will change when moving to ES6 modules, this
seems like a good moment to start that transition.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2375>

lint/eslintrc-legacy.yml

@@ -18,4 +18,7 @@ rules:
   jsdoc/require-param-description: off
   jsdoc/require-param-name: off
   jsdoc/require-param-type: off
+  object-curly-spacing:
+    - error
+    - always
   quotes: off

lint/eslintrc-shell.yml

@@ -12,9 +12,6 @@ rules:
     - mode: minimum
       beforeColon: false
       afterColon: true
-  object-curly-spacing:
-    - error
-    - always
   prefer-arrow-callback: error
 
 overrides: