workspace: Reduce spacing between window previews

With the window titles no longer being shown as part of the previews
grid, we can reduce the spacing to have more space available to the
window previews themselves.

https://bugzilla.gnome.org/show_bug.cgi?id=783953

data/theme/gnome-shell-high-contrast.css

@@ -1094,13 +1094,11 @@ StScrollBar {
   padding-bottom: 32px; }
 
 .window-picker {
-  -horizontal-spacing: 32px;
-  -vertical-spacing: 32px;
-  padding-left: 32px;
-  padding-right: 32px;
-  padding-bottom: 48px; }
+  -horizontal-spacing: 16px;
+  -vertical-spacing: 16px;
+  padding: 0 16px 16px; }
   .window-picker.external-monitor {
-    padding: 32px; }
+    padding: 16px; }
 
 .window-clone-border {
   border: 4px solid #215d9c;

data/theme/gnome-shell-sass

@@ -1 +1 @@
-Subproject commit d0f74b58c31ef48caa93ae8d378f88903ac0e854
+Subproject commit b178ba1d9d090e269b898952fd5a79c54ddc6f75

data/theme/gnome-shell.css

@@ -1094,13 +1094,11 @@ StScrollBar {
   padding-bottom: 32px; }
 
 .window-picker {
-  -horizontal-spacing: 32px;
-  -vertical-spacing: 32px;
-  padding-left: 32px;
-  padding-right: 32px;
-  padding-bottom: 48px; }
+  -horizontal-spacing: 16px;
+  -vertical-spacing: 16px;
+  padding: 0 16px 16px; }
   .window-picker.external-monitor {
-    padding: 32px; }
+    padding: 16px; }
 
 .window-clone-border {
   border: 4px solid #215d9c;