change(tokens): updated z-index tokens with negative values

- bumped the variable values to catch most values we use in our less now
- index important is now capped to 9999
- z-index 0 is now -1, we can simply use 0 if we want to use 0 value without a variable

theme/themes/eea/tokens/z-index.less

@@ -1,7 +1,12 @@
-@z-index-0: 0;
+@z-index-000: -100;
+@z-index-00: -2;
+@z-index-0: -1;
 @z-index-1: 1;
 @z-index-2: 2;
 @z-index-3: 3;
 @z-index-4: 4;
-@z-index-5: 5;
-@z-index-important: 2147483647;
+@z-index-5: 10;
+@z-index-6: 100;
+@z-index-7: 200;
+@z-index-8: 1000;
+@z-index-important: 9999;