Reduce brightness of grid item highlight

Also show theme settings for the view item in the Theme Preferences.
Called it "Data-View Item" for now, to be evaluated.

release/datafiles/userdef/userdef_default_theme.c

@@ -194,7 +194,7 @@ const bTheme U_theme_default = {
     },
     .wcol_view_item = {
       .outline = RGBA(0x2d2d2dff),
-      .inner = RGBA(0x4B4B4BFF),
+      .inner = RGBA(0x303030ff),
       .inner_sel = RGBA(0x4772b3ff),
       .item = RGBA(0x4772b3ff),
       .text = RGBA(0xccccccff),

release/scripts/startup/bl_ui/space_userpref.py

@@ -1221,6 +1221,7 @@ class ThemeGenericClassGenerator:
             ("Scroll Bar", "wcol_scroll"),
             ("Progress Bar", "wcol_progress"),
             ("List Item", "wcol_list_item"),
+            ("Data-View Item", "wcol_view_item"),
             ("Tab", "wcol_tab"),
         ]