[OsSettingsLanguages] Update margin-inline-end for cr:add icon

It's 12px in figma but the icon has some space by itself, so reduce
it to 8px. UX approved (http://screen/wRVCzrD4gDoQvmo) and seems
consistent with http://go/cros-ux-text-button-inner-layout

View of Add Input Methods: http://screen/3ESJMTZJkJuf5zy
View of Add Languages: http://screen/7FrqMDeEtWG6pds
Spec: http://go/cros-lang-settings-figma

Bug: 1113439
Change-Id: Id381b58ac38ecffac6896b34bc1572f7d95e483b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2423751Reviewed-by: Regan Hsu <hsuregan@chromium.org>
Commit-Queue: My Nguyen <myy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809547}

chrome/browser/resources/settings/chromeos/os_languages_page/input_page.html

@@ -65,6 +65,10 @@
         margin-inline-end: 10px;
       }
 
+      iron-icon[icon='cr:add'] {
+        margin-inline-end: 8px;
+      }
+
       /* The default implementation of the actionable list item makes the
        * entire list item row a button such that clicking anywhere will
        * activate the action of the list item. The input method list behaves
@@ -100,7 +104,6 @@
 
       #addInputMethod {
         --iron-icon-fill-color: var(--cr-link-color);
-        margin-inline-end: 4px;
         margin-top: 16px;
       }
     </style>

chrome/browser/resources/settings/chromeos/os_languages_page/os_languages_page_v2.html

@@ -46,7 +46,7 @@
 
       #addLanguagesIcon {
         --iron-icon-fill-color: var(--cr-link-color);
-        margin-inline-end: 12px;
+        margin-inline-end: 8px;
       }
     </style>